Hi!
Well, it depends on what would you like to do on your PC. How much RAM do you have inside? If you're 'round 64 MB, try Damn Small Linux (
www.damnsmalllinux.org). It is a lightweight distro with amazing performance and you have the applications for your common daily needs - word processor, spreadsheet, PDF viewer, web browser, e-mail client and so on. There are also some "light" distros, like Puppy or Vector for example.
Greetings!
Robert