The method I used was to create a shortcut to ZC and ZQuest, then I opened up the shortcut's properties and, under the shortcut tab, modified the target. The methods to do so can be found by right-clicking on ZC/ZQuest (and then the shortcuts) and looking for the appropriate option ("Create Shortcut" and "Properties", respectively). Also, if ZC/ZQuest is in your programs menu, you can open the properties of those links and modify them instead.

It should be sufficient to add "-windowed -res 512 448 big" (without quotes) to the end of what's in the target box for ZC; for ZQuest, just add "-windowed".

When you use the shortcut, the program will start in a window instead of fullscreen.