Boot Camp creates a secondary partition on your internal hard-drive, in order to allow you to run Windows XP/Vista (and several Linux distros I reckon) natively. That is, when using Boot Camp, you can run OS X OR Windows/Linux only. That is, the only requirements for you to use Windows/Linux is for your hardware to meet the minimum requirements of the OS.
Windows Vista Minimum | Recommended Hardware Requirements
Processor 800 MHz | 1.0 GHz Memory 512 MB RAM | 1 GB RAM Graphics card DirectX 9 capable | DirectX 9 capable GPU with Hardware Pixel Shader v2.0 and WDDM 1.0 driver support Graphics memory 128 MB RAM supports up to 2,756,000 total pixels (e.g. 1920 × 1200) or 512 MB+ for greater resolutions such as 2560x1600 HDD capacity 20 GB | 40 GB HDD free space 15 GB | 15 GB Other drives CD-ROM | DVD-ROM
If you are looking for a way to run OS X AND Windows/Linux at the same time, check out VMware Fusion or Parallels.