Here's a few ways to speed up Windows XP and save resources and hard drive space without installing any programs. This does work to speed up Windows7 and Vista, but these steps are for the XP platform.
1) Disable Thumbnail Cache
If you don't view a large database of photo's frequently, you can safely disable this. All it does is create a hidden Thumbs.db file that stores a cache of thumbnails for all pictures that was ever in that folder, regardless of if the image was deleted. So this file can grow large depending on how many images you have in that folder. These .db files are created in every folder that has images in them.
To disable go to My Computer, Click Tools->Folder Options, Click on "View" tab, Check the box that says "Do not cache thumbnails". Click Apply and OK.
2)Turn Off Indexing of your hard drive
Windows indexes all the files on your hard drive and stores it's location, so it waste's space by saving this information and resources by indexing when the computer is idle.
If you use that 'Search' function in Windows to find files or folders once or less a month then you can safely turn this off. You will still be able to use this search feature but it will take a little bit longer, which is worth it to me.
To turn it off go to My Computer, Right-Click on the C: Drive, Click Properties, Uncheck Allow Indexing and click OK, its ok to skip files(you will know if you get prompted)
Do this for each Hard Disk Drive(C:,D:,E:, etc.)
You can do even better by also disabling the Indexing service. Go to Start, Run, type services.msc, look for "Indexing Service" Right click on this service, Click Properties. Click Stop and change "Startup type" to Disabled. Click Apply and OK.
3) Disable System Restore
If you're smart enough to do a fresh install, you should disable this service. System restore creates restore points periodically and every-time you install or uninstall a application, that is a lot of wasted space. And uses a lot of resource's when its creating these points.
To disable system restore Right-Click on My Computer and Click Properties, Click on System Restore Tab, and check the box that says Turn Off System Restore on all drives.
Now these 3 steps wont make your computer super fast, but will free up some resources and hard drive space for you.