I agree with Ashmasterash. Make sure you have the latest graphics drivers. Also make sure you have the latest drivers for your motherboard. This could include a hard drive controller update that could give a good speed boost. It could also include a BIOS update. A BIOS update can improve performance and boot-up time, but if something goes wrong during the install, it can break your motherboard, so be careful if you are installing a BIOS upgrade.
Also, consider some more RAM. While this isn't free, it shouldn't be more than about 50 bucks to bring your computer to 4GB or the maximum it allows (whichever is less). Check out http://www.crucial.com to find out what kind of memory you use and what the most you can install is.
Note that this all assumes you're already running at more or less peak software performance. Run a spyware/adware sweep (using AdAware or Spybot). Also make sure you have anti-virus software and that it is up-to-date. And make sure you have the latest system updates (from Microsoft). Delete any programs you aren't using (using the Add/Remove Programs tool in your Control Panel). And if you have any programs that launch at start up (other than your anti-virus software), turn those off (usually this can be done in the program's settings or by removing it from the "Startup" folder in your start menu).
Finally, if you do have a lot of adware/spyware/viruses/malware, you might consider reinstalling your OS (Windows) from the disk it came on. With Windows, I recommend doing this every 18-24 months at least (depending on who is using the computer and how much).
Following these steps can vastly improve your computer's speed in some circumstances. Hopefully that helps!
Good luck!