Tascam's GS phone registration person couldn't answer this question. Maybe someone here can: I have GS96 on my computer. I purchased GS160 to upgrade to GS3, but need to register GS160 (and get a registration number and all that) before I can purchase the upgrade. Is there a way I can register GS160 without installing it, and jump directly to GS3? (I'm in the middle of a job and I don't want to mess up a working GS system. GS3 will go on a new computer)
Upgrading from GS96 to GS160 is very low risk. It's fast and painless. As I recall the GS160 disks are v2.53, which has everything except for the hammerfall bug fix (a simple MIDI filter to remove unexpected MIDI controls). Basically, if msg32 is working well for you with GS96, moving to GS160 will cause no surprises.
For an extra margin of safety, copy all the files from the CD to the hard drive, then install. To be super safe, do a scandisk after copying the files and before the installation. That way you don't get half way through installing the new files, and then find that some odd file can't be read from the disk.
GS3, on the other hand, may or may not work out of the box. It's well worth the upgrade IMHO, but if you're in the middle of a production, I'd recommend getting a new system disk, installing a fresh version of Windows and installing GS3 on top of that. If it works, great! If it fails, go back to your old drive until you've got time to troubleshoot your system with GS3.