by WhiteRider » Mon Jan 30, 2012 4:28 am
1) As long as the old installation is never run again ( as it clearly won't be in this case) it shouldn't cause any problems.
2) 9.1 is still pretty new and has problems so we do not recommend/support it yet.
9.0 has a 64-bit version and if you're installing fresh then we recommend that version. You'll get a slight performance improvement, although we don't have any figures - probably not enough to justify upgrading if you have a large database, but if you're just starting up then it's advisable.