Most novice's seem to be incapable of installing any OS (Linux, Windows, BSD, ...) except perhaps one from Apple.

Gentoo, Lindows (Linspire), and Xandros are probably the best for this situation. The latter two especially should be easier to install and configure than Windows.

Knoppix is my favorite, but it is intended to run completely from CDROM, so some expertise will be needed for persistent storage of email, preferences, etc..

Cheers