Configuring XFree86 to use your mouse, keyboard, monitor, and video card correctly used to be something of a black art, requiring extensive hand-hacking of a complex configuration file. No more; recent releases have made the process nearly trivial. It simplifies matters a lot that there are no longer separate servers for different kinds of cards, just modules loaded by a common server.
If you're enabling X as you intall a Linux distribution, the distribution install script will ask the few questions needed to configure X. Otherwise, all you need do to configure it is fire up the command XFree86 -configure.
Both methods depend on the fact that all new PC hardware these days ships with monitors that can tell X what their capabilities are. When invoked in this mode, X does that query and also polls your hardware for the presence of a mouse and keyboard. It then writes out a configuration file thar is used by later runs of X.
One minor point to keep in mind is that, if you're like most people using a current PC, your keyboard is actually what XF86Setup calls `Generic 102-key PC (intl)' rather than the default `Generic 101-key PC'. If you pick the default (101) the key cluster on the extreme right of your keyboard (numeric keypad and friends) may stop working.