Reinstalling Windows

Reinstalling Windows to "wipe it clean and start over" implies, well, wiping it clean and starting over - so yes, you will need to reinstall drivers and software. Don't forget to back up your data beforehand!

Make sure you go into the bios and remove the partitions you have for windows. It is possible to reinstall windows without actually reformatting which isn't what you want.

before doing the full wipe, which windows do you have? i assume windows xp?

go to ccleaner.com and get it. do a complete cleanup of your pc (files and registry)

go to defraggler.com and do a full defragmentation of your disk (not just files, the whole disk).

if that doesn't speed up, yes, you can try a reinstall.

often those two steps are enough that a pc works great again afterwards.

Also, if you use SCSI or SATA drives, make sure that you either have a floppy with the drivers (For Windows XP) or that your controller is allready supported by the installer (Not that common unfortunatly), Alternativly you can create a new install CD that includes the drivers. (This is less of an issue with Vista since it can load drivers from a CD during installation)