This is a funny story, and I thought I'd tell everyone about it, because this is something that has been driving me insane for MONTHS and the solution was so freakin simple.
Anyway, the big problem I've been having with Vista is my screensaver not working since build 5381, it just would not kick in, I Checked everything, made sure there was nothing preventing the system from idling etc.. I was playing around the other day and it hit me. Right after 5381 was released, I bought a Microsoft Laser Desktop 6000 KB/Mouse combo. No, it can't be that I thought. Well just for kicks I plugged the PS/2 portion of the wireless reciever in for the keyboard and left the USB as was (essentially making the keyboard PS/2 and the mouse USB). Still no screensaver, so I figured, OK let's yank the USB plug. 2 minutes after yanking the cable the screensaver kicked in. It was the mouse the whole time. Solution? Went out and got myself a Logitech G7 Laser (AWESOME Mouse btw, and the setpoint software works on Vista).
And for anyone wondering, I did some research into the problem, apparently this issue affects any machine running Media Center with this keyboard/Mouse combo. If you kill ehtray.exe, the screensaver will kick in, but then your MCE Remote won't work.
Bottom line, don't buy Microsoft hardware, lately they can't even get it to work right with their own software it seems.