xp/w2k:
Right click My computer.
properties
Advanced tab
Startup/recovery
In Xp I believe they allow you to edit boot.ini.
in w2k they don't.
in xp, you can edit boot.ini, and remove the other os.
or as with w2k, select the default os, and either uncheck the display list, or set it to 1 second timeout.
Alt method with w2k is to manually edit the boot.ini file (you need to unhide it first), or boot the cd, start the recovery console and edit the boot.ini file there.
if you manually edit, the order in the list is the order of the display of choices. if you need the 2nd choice, then delete the entire line for the first one. the line will look like this:
multi(0)disk(0)rdisk(0)partition(1)\WINNT="Microsoft Windows 2000 Professional" /fastdetect