RH is a good way to get started with linux, as is mandrake. However, the latter is not something that i particularly enjoyed using, though it did let me know that I could deal with linux. RH is convenient b/c it is well supported, gentoo is better now than it was a year ago b/c they do make binaries, but compiling is such a waste of time, given the marginal benefits. I am in much greater need of using my computer than spending time optimizing it. Having played with the above, I turned to Debian. I had a good bit of trouble getting it up and running (but b/c i was totally doing somethign stupid and have a fairly obscure hardware setup) but once it was up, it has been extremely easy to maintain and run whatever I want on it.
Given the machine described, compiling with gentoo will take FOREVER, don't do it. RH and Mandrake will consume some massive resources. Given that, I'd use debian (but then, when wouldn't I use debian?). <3 apt-get