I'm not sure if this will work in Win2k, but I know it works in Win98.
1. Right click your D2 shortcut and go to properties
2. In the "Target:" box, add "-w" (without the "

to the end of the path that is already there. Make sure you add it OUTSIDE of the quotation marks surrounding the path.
3. Press ok, and play D2 in a window
Good luck
-Tom