Symlink or Symbolic Linking, is a way to speed up load times of multiple copies of wow, buy branching off heavliy used directories(wtf) and utilsing shared directories for common files (inteface and data). It basically allows you to run 5 copies of wow from one folder as if it were only one instance running.

Symbolic links - vista is a linkk for setting this up in Vista. To perform the same in XP you need to search for Junction linkning