Restoring my netbook back to the out of box condition?

When I recently bought my Eee Pc it was originally on Linux.
And I reformatted the hard drive and installed windows xp.
Having had xp installed am finding that it's too much of a drain on resources.
What want to do is reinstall the Linux gnu (i think) back onto it.

As I bought the unit 2nd hand there's no recovery cd.
I've looked online and can't find where or how to download it.


Can somebody please send me a link, or tell how to download, as I find Linux baffling.