I have 2 drives with xp on each drive. How do I remove the os on one drive without screwing up the other drive?

As far as I'm aware, Norton Partition Magic can do this, you can manually merge the partitions that the Windows are on. Unfortunately this is not free, but you can download a trial from Here.
Hope this helped. If you need further instructions on how to use the program, do not hesitate to pm me.