dual boot with xp and windows 7: soundmax installation in one OS botches install in the other

I don't see a windows 7 beta ng, so I'm posting here since 7 is so closely
related to Vista.

The problem is simple: I've an Asus P5b Deluxe with Soundmax, and it works
ok on XP Pro sp3. I've just set up a dual boot with Windows 7 on another
hard drive, and all works well except for the fact that when I install the
Soundmax drivers on 7, the installation on XP is corrupted, I'm told I need
to uninstall and reinstall, and then that corrupts the install on windows 7.
Etc. The Soundmax install doesn't give me an install directory option, but
I'm surprised that, since XP and 7 are on different hard drives, that they
are messing each other up. Any way around this? Thanks.
Bill