The best way to accomplise that is to use pmagic within your win9x ( xp or whatever ) delete the partition and resize the actual one
And then get the win98 boot cd ( cause this is the only one with dos prompt ) (xp aint having none,dos at all,just cmd) and boot in command prompt ( not the setup nor w/o cdrom support )
At the prompt Write : fdisk /mbr ( mbr=master boot record ) which saved my a*s couple of times
Then the only OS that'll exist ( and boots auto ) will be your 1st one.
Farewell friend.