Every script should be able to be running on all Windows OSs. If some VP fails on Win2003, but it passes on XP, then you should find out OS version using function SQAGetSystemLong. For more info about this function look at help.
If you want to give somebody a fish, you'll do better if you teach him how to catch it.
There are some issues connected with OS version. For example - in different OS there come MMC of different versions. So you can have problems while working with mmc (I had some).
As for scripts - there no matter for them to run on winXP or on win2k3.