Well if everything on said hard drive is needed absolutely then you should just buy an external hard drive with USB 3.0 and store some files on that

If its anything but disk drive C, and you dont really care about whats on it;

1) Open my computer
2) right click the drive
3) left click format
4) check quick format
5) Hit ok/start and watch the fireworks.

That may be something about temporary files. Download something like CCleaner, run it on your system. Then if it's already something like an external drive, just format it like ShatteredSoul said a post ago. But don't do that on your system part.

get some water and soap, clean it. bam now your drive is brand spanking new.

OT:
If you want to delete everything on it (don't do this on the C drive) :

1) go to ''My Computer''
2) Right Click on the drive you want to format
3) Click on format
4) Check the box that says quick format
5) Hit start and wait to complete (go play a game or eat a cookie)
6) Profit and lot's of space.

delete system32.

Well that cleans up nicely , but then the PC will not be functional xD

Simply run 'Disk Cleanup' - It will delete everything that has not been used for over a month.

If you want your computer Compleatly cleaned for a game Or something
Factory reset.
takes your computer back to the way you go it.. even if it was second Paw.

How big is your HDD anyway? 160GB? 250GB?

Run CCleaner and delete whatever you don't want.

I would advise to do a defragmentation. After it finish, you should have like 20GB more space.

I dont think Defrag works if your below a certain amount of disk space. To OP, you could check and see if you have old system restore files which may be taking up space. This is under Start -> Accessories-> System tools -> System restore, you might be best deleteing all but the most recent restore date. It might also be advisable to take a look at a little program called tree size, it tells you whats taking up the most space on your hard disk. link: jam-software.com/freeware/ , just be sure not to delete any key system files though.

~scotty

There are programs for this right?

First use a program called CCleaner. It cleans your computer for unnecessary/temporary files. Then you should check what progs/games you don't need. You can do that really quick and simple by going to controlpanel -> Programs -> uninstall a program (on W7/Vista). Then you get a list of your programs and games, and you can easily uninstall stuff from there. After this I recomend to do a defragmentation. You can use a program called Defraggler for this. It sorts your files and put them in one end of the harddrive, and makes your pc work better. (I'm not sure if it really helps on SSD's)
Hope this helps

Good to know Glad we managed to help you.

uhh try system restore that is destructive, it is different on each computer so i can't help anymore than that...