Fonts have been the number one complaint I've heard about linux especially when dealing with web browsers, they're not quite as pretty as XP's Cleartype fonts. But, KDE (basically a desktop for Linux) does support font anti-aliasing and it is pretty easy to copy over your windows fonts if you're dual-booting (in Mandrake at least). Red Hat does not try to be a desktop OS at all while that is Mandrake's main goal. Since Mandrake is based on Red Hat, they are very similar at the core (more so than a lot of other distros). You should have no problem finding support online for either one.
Right now I dual-boot XP and Mandrake 8.2. I tend to spend more of my time in linux because I love having the ability to tinker to no end as well as the enormous amount of free quality software available. Mandrake's collection of graphical tools also makes this much easier to get into for the first time user. Windows on the other hand tends to hide things from you and discourage tinkering. If I dont like XXX software and I can remove it in 10 seconds from Mandrake whereas in Windows it takes 100 CS professors and US attorneys to claim it can be done and 1 guy whose name rhymes with Yates to say it cant and would cause the demise of western civilization if it were.
As far as gaming (and windows software in general) goes, WINE and WINEX are both making significant strides. WineX is done by transgaming (www.transgaming.com) and claims near perfect support for Diablo 2, Max Payne, and The Sims. They also have pretty decent support for _tons_ of other games. Codeweavers has put out two packages based on Wine to support allow you to use all the plugins you would typically need for web browsing (Windows Media, Quicktime, Shockwave, and MS Office viewers). Real Player and Flash plugins are available natively for Linux. Codeweavers also has a package to allow seamless install of MS Office 2k. The codeweavers stuff has a demo version available but the full costs $25 for the plugin stuff and $50 for the office stuff (I think) and transgaming is $5/mo if you want access to the easy to use packages. While these packages are not necessarily free, it is still cheaper to download a version of your favorite distro and purchase the codeweavers crossover plugin and a subscription to transgaming than it is to buy XP. I dont see too much of a reason to buy the office support right now since there are several free office programs which work quite well. Wine, which all of this stuff is based on is free in its basic form also.
There are also some pretty cool games writtenly specifically (well they're not exactly Black & White but they're still cool). Be sure to check out Tuxracer, Chromium, and Frozen Bubble (All included in Mandrake 8.2). They're not the most complex games in the world but they've consumed far too much of my life since I installed linux.
I would go with Mandrake if you are looking to run a desktop OS and it is your first time using Linux. Red Hat is not really trying to be a desktop OS. In fact, the founder of Red hat has said in several interviews that he does not believe thats where linux will end up nor should it focus on being that. While you could in theory make the OS whatever you want, in practice its much easier to go with a starting point, such as Mandrake, thats more in line with your goals (I assume you are looking for a desktop) and will work on better satisfying them in the future.
And thats all I have to say about that
I've taken more good from alcohol than alcohol has taken from me --Twain