Steam causing major slowdown

Nineteen Hundred

Just as the topic title says, Steam slows my comp down to the point where it's unusable. I just put my new rig together yesterday, and just got around to testing its gaming capability today. When I first installed the Orange Box, everything ran just fine. My computer worked perfectly and I could play games with no problems. However, after I had to restart my computer for some reason, it practically came to a halt. I'm not sure how I figured this out, but forcibly ending Steam through the task manager (doing it normally wasn't an option), everything went back to normal, unless of course I tried to open Steam again. Uninstalling and reinstalling it worked until I restarted the computer again. I have no idea where to begin figuring this out.

When I did manage to get the window open, thought, my games tab would populate. Just got an endless "Steam is checking for games updates." Same deal with the media and tools tabs.

My build, if that helps:

Asus P5N-D 750i Motherboard
Intel Core 2 Duo E8400 @ 3.00GHz
2GB Corsair XMS2 Dominator RAM
Zotac GeForce 8800GT
Windows Vista Home Premium 32-bit

Nineteen Hundred

An update and... bump, I guess: I just figured out that Steam will load and run normally if I remove the game content from the 'steamapps' folder. On a whim, I restored everything in the folder except the 'winui.gcf' file. Steam would run and the game list would populate, but the program (thought not the rest of the computer) would hang frequently and for 30 seconds or more at a time.