You could install any LInux distro you wanted on that system. I would only steer clear of Gentoo due to your lack of experience, and low system RAM. I would also use a lightweight window manager such as fluxbox or xfce, since you have a 650MHz processor. That being said, now you have to choose amongst 99.9% of all the thousands of Linux distros that fit the requirements you have stated. (As you can see, Linux is more forgiving on older hardware.)
What are you trying to do with your system? Workstation? Server? School work? Home business? General web surfing?
For newbies, I generally recommend a distro that runs off CD so that you can "try before you buy". Mepis and KNoppix are two common ones. If you do not have broadband Internet, or if you do not have a CD burning program like Nero, you could buy Suse from Best Buy or your favorite computer store, or you could buy a "Fedora Linux" book that has CD's inside.
_________________
Currently using: Slackware 10.0, Fedora Core 2, Windows XP Tablet
Previous distros and OSes: Red Hat 7.3, 8.0, 9.0, Fedora Core 1, Mac OS 10.2.8, Mac OS 10.3.1, Yellow Dog 3.0.1, FreeBSD 4.7
Emage industry lists Local lists