Boot Camp is a MacOS X.5 Leopard feature that manages to install a (licensed) Windows XP or Vista operating system on a Mac computer in a dedicated partition.
A program called Boot Camp Assistant helps in creating a new disk partition on a Mac machine keeping all the data safe. When Windows is installed on that partition, the drivers needed can be found on Leopard DVD.
Boot Camp installs a bootloader to choose the operating system to load. It can be run at startup by pressing ALT button. Boot Camp even provides an automatic PC Key remapping program.
All the drivers Apple provides are Microsoft WHQL-Certified.
This program used to be a public beta before Leopard's final release. Now it continues to work on Tiger systems but can't be downloaded any more from Apple's website nor it is supported on any OS than Leopard.
From early version of Leopard, it seemed that one could perform a system hybernation on both system to fast-switch between the two. Now this feature is not present.