Removing OS

If a HD has 4 partition and each partition is loaded with different OS with bootable options at the startup Ex. WinME on 1st, Win2000 Prof. on 2nd, Win2000 Adv. Server on 3rd and WinXP on 4th. Now If we want to remove one/two/three OS without disturbing other OS settings how is it possible ? Kindly Explain in Details ?