Run, do not walk, but run to Ubuntu and check it out.
Download the latest version (7.04 as of this writing, aka "Feisty Fawn"). It's only a 700 Mb file that you extract onto a bootable CD. Test run it straight from there without impacting your existing machine... if you like, then install it permanently using the shortcut provided.
Quick, easy, and very user-friendly (contrary to any previous Linux stigma). As with any Unix-based system, it runs much more efficiently *and* securely than that disease laden petrie dish of an OS from Redmond.
If you're not ready to switch over completely, breathe some life into an older PC by installing Ubuntu there. You'll be amazed at how quickly it can perform on older chipsets with even 512 Mb RAM.