Windows boxes without Quicktime installed will play .avi or .wmv files. Unless you have the Flip4mac Windows Media encoder component installed on your FCP machine, you’ll need to export .avi files with an appropriate codec.
Windows boxes with Quicktime should have no trouble with any Quicktime .mov files that you export from your FCP machine.
If you’re working with NTSC DV material in FCP, make sure to resize your clips to a square pixel aspect ratio in order for them to appear correctly on computers. Full-resolution would be 640×480 square pixels (as opposed to NTSC DV’s 720×480 nonsquare pixels). Any reduction in frame size should conform to a 4:3 aspect ratio, assuming your source material is 4:3 and not 16:9 – i.e. 480×360, 320×240, etc.
Some more information regarding delivery would be helpful. Are the clips going to be files transferred locally to Windows machines, or delivered via the Web? Obviously compression issues become much more important for web delivery.