Bah, almost finished a huge reply when I load some ****ty site full of bad java which crashes my browser. Arse. So the following is a quick resumé of what you might want to look out for.
Processor: First rule is, don't buy the top of the range model. The slight increase in performance isn't worth the much larger extra cost. Whatever you choice, go Athlon (Socket-A mobos) - they tend to be much faster and more stable than Pentiums, but can run slightly hotter, so buy a good heat sink (and remember to attach it with thermal grease!).
Personally, if I were to build myself a new computer now I'd run an Athlon 1.4 GHz, but if you want to stay future proof for games, you will want a faster one.
Mobo: this is the core of your system, and the thing you should pay the most attention to, as if you buy a good mobo it will make upgrading much easier and cheaper. Machines are upgradable; it's just pre-made computers have built in redundancy so you'll keep buying another computer whenever you need to upgrade. Abit and Asus tend to be good. Some mobo features you may want to look out for:
Dual processor support: expensive, but dual 1 GHz Athlons will give you blistering number crunching (typically much faster than a single processor with twice the power), and more reliable to boot, especially if you're runnig a tried and tested design. Responds like a beaut to overclocking.
SCSI support: again, expensive (very in fact - a 36 GB 10,000 rpm Seagate Cheetah will cost me over £300) but it means you'll have access to the fastest HDD's, CD's and DVD's on the market. If you're planning on running Linux or any other *nix clone, you'll get an even higher performance increase.
RAID support: if you're running standard EIDE drives, RAID (Redundant Array of Inexpensive Discs - running two or more identical discs in tandem) will either give you increased protection against data loss (good for long term large scale storage; essential for running a server) or a large increase in access times.
EIDE support: if you're runnig standard EIDE HDD's, get a mobo which supports at least 6 EIDE/ATAPI devices. This will let you install two hard drives, a DVD, a CDRW and a zip drive and still have space left over.
If you want to save money on HDD's, buy a small yet fast 5 GB 7,200 with a big RAM cache to install your OS and progs on and a slower 60 GB 4,200 rpm slave to store all your files on.
Make sure your mobo supports UDMA - this will speed up your hardware no end.
USB support: as it's ubiquitous these days, get a mobo with at least four USB sockets (some hardware doesn't allow you to daisy chain). USB 2 support is good too, but it's not a patch on firewire.
Firewire support: essential if you're thinking of doing any digivid editing, or external storage over 1 GB (say, an external hard drive) - one socket should suffice.
RAM: get a board which has at least four slots and is expandable to at least 1 GB. You'll want to start with as much RAM as you can afford (preferably 512 MB) as the speed increase you get is phenomenal, due to the system writing to the hard drive less. It doesn't matter a whole lot what type of RAM you get, since the speed is limited by the system bus - which should be at least 133 MHz, pref much higher.
Ethernet: If you're planning on runnig a home network of any kind, then an ethernet is an absolute must, and it it's mounted on the mobo you've saved yourself a valuable PCI slot.
Slots: a board with lots of free PCI (and maybe AGP if you plan on running two monitors and looking dead cool
) slots (at least 4) will anable you to install a truckload of new hardware. If the mobo supports all of the stuff you need (like firewire) you'll still want at least two free slots. It's likely that the mobo you buy won't have all the features you want, so the more slots you have the more future proof you will be.
Extras: Don't bother paying extra for mobos with on-board sound and graphics; you'll be buying a video and sound card anyway.
Make sure you buy a case speaker, so your computer can beep in case you need it to - this will come in very handy if things start going wrong.
Make sure you buy the right cables and connectors!
Remember to attach the CD audio cable to the mobo, else CD audio will be played down the EIDE/ATAPI cable, which is a total waste of resources.
Make sure your mobo still has support for serial, parallel and PS/2 ports; if they don't, you'll lose access to alot of hardware (and remember the parallel port is f**king fast). USB keyboards and mice are overpriced, and the mice tend to be rater choppy to boot. Go PS/2.
Case: Sadly overlooked by most people, the case is very important. Buy an ATX case - for best access, upgrade and air flow buy a tower, and if you want to keep cool buy an aluminium one, which can be picked up relatively cheaply. Remember if you buy an aluminium case, not only will it come with zillions of expansion ports, but it will last you for your next two computers too. Case fans are good for keeping your overclocked Athlons and 10,000 rpm SCSI's in tip top temperature.
PSU: This has got to be the most overlooked part of a PC ever. For most people, a 300 W power supply is a good bet, but if you're running a dual processor (modern processors can easily draw 100 W), lots of devices or lots of cooling fans (naughty overclocker you!), then a 450 W PSU will be better. Nothing would be worse than setting up your computer and then finding out you only had enough power to run 80% of it - in fact this will often cause write erroors to the HDD's, resulting in goodbye computer, and a whole new reinstall neccesary.
Once you've got ALL your hardware assembled, tot up the total power consumption of them all - then add another 50 W to this, and you should have a good starting point over how powerful yours needs to be.
Modem: Right, now this is really important: DO NOT BUY A SOFTWARE MODEM! BUY AN EXTERNAL HARDWARE MODEM! Most modems these days are cheap software winmodems; they emulate what modem chips should be doing in the software instead. This is an uneccesary and large drain on your processor, and some of the poorer winmodems out there will crash your whole OS if the CPU goes over a 50% load for any amount of time. If you're using dialup, but an external hardware modem. They're considerably more expensive, but a) you will get a sligtly faster connection (depending on your phone line) and b) you don't run the risk of software crashes killing you computer and c) you free up alot of processor resources; winmodems have atendency to have horrible drivers. You can get internal PCI proper modems, but these are quite expensive.
Right, that's all I can think of so here are a few links:
Eclipse - good UK hardware site. Will give you a good selection of what's out there, as will
www.pcindex.co.uk
Tweak3D's guide to making a computer
A very comprehensive BYO guide
Some more techy data on BYO
Hope this is handy. Rmember, if you want to make your computer totally future proof - start using Linux! I'm going to make myself a local server/firewall with an old pentium 2 machine and that's way more power than I actually need. Huzzah, huzzah, go OSS!
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