ok, here we go!!! congrats on chosing linux!
first of all, mandrake and redhat are both very easy to use but have very different feels: depending on your needs, u should make your decison
mandrake is very user-friendly and very easy for those to make the switch from windows to linux: lots and lots of userfriendly (and pretty well-developed) os and hardware tools but my biggest gripe is just its feeling of being a newbie "childish" distro and the fact that it doesn't automatically install many of the libraries needed to install programs; in other words, very easy to learn and use
as for redhat, i definitely love the feel, a very professional feel, but the biggest gripe of most people is it's way of doing things: that is, it does many things similar to the way that m$ does things (most of us here bash windows) both in business ways and software ways (it even has its own add/remove programs utility); other than that, it is a very "cool" distro that has enough advanced features for those who are willing to learn them and decent user tools (but don't depend on them); the only reason i don't use it much is because it doesn't support my sound card
advice: learn about partitions, get good partitioning software (partition magic is the best IMO), do some background reading on the way linux does things; learn some basic commands and u should be set (this is the way i got started with linux)
i started with redhat with a very good footing: if u can, download and read the redhat9 install manual, it has some very good information, especially the appendicies
oh, and some more advice, make sure you have compatible hardware so that u won't have to pull out your hair trying to figure out how to get them to work
and now, make your decision and have fun with linux!