So your multiple monitor support is just OS standard built in, or some software you installed from you video card maker?
I just reinstalled the ultramon on my XP box here at work.. Got tied up with "work"
so couldn't test your scenario.. But real quick it allows for buttons that real easy move windows between monitors on the title bars of the windows. So you click and bam its on the other window, etc. etc. This is the feature I most used, and now that I have it installed will start using again