Because linux is open source, everyone and his brother modifies it and re-releases it. Linux is itself just a kernel, and that is actually quite standard and available from kernel.org. However, what you want is not a Linux kernel, but a Linux distribution, which includes the Linux kernel and a bunch of other tools (mostly made by the GNU project).
There is no single standard distribution, although all of them use the same standard kernels. The most popular distribution right now is called Ubuntu. The other major distros are Debian, Gentoo, Red Hat, Fedora, Mandriva, Slackware, and a few others I'm probably forgetting atm.
Ubuntu is a good place to start for a beginner. Gentoo is my personal favorite and it's what I use, but the install is daunting (while the Ubuntu install is trivial / automatic).
You can play a lot of direct x games using a program called cedega. It is not free though. Performance is usually pretty close to what you get in windows. However, some simply don't work quite right, or don't work at all. Games written for linux are just as fast or faster than the same game in windows, but games that are written for windows and emulated tend to be buggy. (Strictly speaking, WINE stands for Wine Is Not an Emulator... it's actually an implementation of the Win32 API and Cedega adds in an implementation of directx.)
Graphics card drivers are readily available for both nvidia and ati graphics cards and quite a few others. The nvidia drivers are excellent and generally of the same quality as the windows versions. The ATI drivers have come a long way but are still somewhat behind the windows counterparts.
