Sharing files over my network, help appreciated

[Angrist]

I'm trying to stream my video files (and music I guess) from my PC to my media streamer, over the network I set up.

Now the streamer does see my PC and I can get to the part where I see my PC and its shared folders... But when I want to enter a shared folder, it asks me for a user name and password.
Edit: Internet works on the streamer btw. I was pleased to find free Discovery Channel and lots of other stuff.

I didn't set a password for sharing stuff. Just pressing OK (without filling anything in) doens't work either.

When I go into the page of my modem, I see my PC in the overview, and something called (null), which says something like this:
IP Address: **.***.1.36
MAC Address: **:**:**:b5:60:a7
Address Source: DHCP
ConnectionType: Ethernet

In the Network screen of Windows (Vista btw), my streamer shows up as a 'Realtek Embedded UPnP Render()'. That doesn't make sense, it's not a Realtek product.





So short story: how do I set up a proper network to share my PC files with another device? Thanks.