If all things in Windows XP that are removable are removed, how much space can be freed?

By all things, it means any components or files that are part of Windows installation. Either by automated uninstall or manual uninstall. Without breaking Windows functionality as GUI based OS. Multi user capability must be kept, so Explorer as a shell is still required. Thus, Windows PE is not applicable.

Answers for Windows Vista or Windows 7 are also welcomed.