Hi David,
When I bought the now defunct Gigastudio 4, it had a 32 and a 64 bit version. I was thinking of moving to 64 bit with Windows 7 and installing GS4 on that, however I note that you state that GS doesn't work in Vista 64. Did you actually try it and find it didn't work, and if so have you since tried with Windows 7 in 64 bit mode?
Derek Williams