You can't really install something "over" an existing distro but you can install something "adjacent" to an existing distro if you've got available disk space. If I understand your question correctly (which may be incorrect) you want to test out 9.1 without damaging your existing installation. If this is correct, this is what I'd suggest you might consider:
1. Backup your important data. Period. This step is critical no matter what you decide to do next.
2. Rather than install v9.1, you can download the Live-CD version of Suse 9.1 from
LinuxISO and run v9.1 off of it during the evaluation phase. If you decide it isn't to your liking, you can simply remove the CD, no harm done.
2. Assuming you've got an extra hard drive, or you have available unallocated disk space on your existing drive, set up your PC as a dual boot system, with Suse v9.0 and Suse v9.1 as the boot choices. Should the v9.1 be unsuccesful, you can just remove that option from your boot manager and drop the partition(s).
3. Assuming you have the v9.0 disks, and that you originally set up /home in its own partition, you could install v9.1 on top of v9.0 but this would kill v9.0. Basically, what you'd do is to install v9.1 as though it were a fresh installation, into your existing partitions, but your would *not* format the /home partition. At the conclusion of the v9.1 installation, you'd be running the new kernel and new versions of the packages, but all of your /home data would remain as is. If /home was not its own partition, at the end of the v9.1 installation you'd have an empty /home directory, but you could easily restore your data by copying your backups into it (ie, Step #1). Should the results be unsatisfactory, you can roll back by re-installing v9.0. Again, if /home was not its own partition, you would need to recopy your backups into it.
Hopefully this is clear; if not, post back.
OT: I just got back from a week's vacation in Dublin -- a beautiful city. Good luck with the project. -- J.W.
