Linux?

I would choose SuSe 8.0 Pro, cept its not free and its like $80. Never tried Mandrake. RedHat isn't bad either. Slackware kicks ass, but its not a beginner choice.

I would give SuSE a try..

SuSE 7.x (7.0-7.3) can be installed from the web if you have a decent connection and don't wanna pay for the whole package.. SuSE 7.0 is available as a eval cd, it's fully functional but not that many programs as with the commercial cd's (full suite).

More to read at www.suse.com