So your windows folder is using 5 GB, and the temp folder is using 3 GB? Do you have (or ever had) a program that has a similar name (any similarities) to those really large files. It is odd that it would do this... my windows/temp folder is only 2.68 MB. What version of windows do you have? I don't think even win Xp takes up all of 2 GB. I think even Xp is under 1 GB, but I'm not sure. You also might want to search around the used computer stores for a lilttle bit bigger HD if you use your computer enough to justify getting a new HD. New will run from $100 to $300, but you can find used 10, 15 GB ones for around $40 or so. I just put together a new computer 2 months ago so the HD was clean when I first got it running, and now I have used 20.3 GB already. Now I use my computer more than the average Joe and have a good portion of my CDs on it (ripped in 320 kbs) so that accounts for alot but that just goes to show that today HD spaced is used up very easily, mostly because HD space is so abundant now and programs are utilzing it. I think my Office 2002 Pro uses 2 or 3 GB, and many other programs use over 1 GB. My sound card takes up 1.4 GB alone. (drivers for it are at least 800 mb)
Another way to find some space to clean is look through all your games (if you have any on your computer) and sometimes programs and see which ones can significantly open space by reinstalling at mininum install, installing to run off CD, or just deleting completly. Also poke around your HD and look for large things you don't need.