Having got my fingers severely burnt with the upgrade from Tiger to Leopard (posted elsewhere), I have decided to be a bit more scientific in preparing my machine for the downgrade to Tiger. As a Windows user for many many years (and still do on desktop comp) I have a good grounding of how to set one up to minimise issues when it comes to reinstalling the O/S. My knowledge in this area with the Mac though is nil. The Mac is a PB G4 1.67 with 80 Gb HDD. Therefore I have a few questions as follows: 1) If I partition the HDD into two, one partition containing the O/S and the other data, can I install/uninstall the O/S at will with no effect on the data partition? 2) Assuming 1) is OK, what would be the recommended partition size for a) Tiger and b) Leopard (I am presuming I will be able to go back to Leopard one day!)? 3) I may take the opportunity during the downgrade process to perform open HDD surgery and replace existing 80 Gb one with a 160 Gb one. Would the recommended partition sizes in 2) change? 4) Am I correct in assuming that you can reformat one partition without affecting the other? 5) Providing there is enough free space on the HDD is it possible to increase/reduce partition size on the fly and if so can that be done through the O/S or do I need some specialist application? (I think this is kind of answered in this thread: http://forums.macrumors.com/showthread.php?t=393400&highlight=partition+size but any other thoughts?) 6) Does the Applications folder need to be in the same partition as the O/S? 7) In Windows, applications are tied to the Registry but no such encumbrance exists in the Mac O/S. If answer to 6) is that the O/S and Apps have to exist in same partition is it possible to back up the Applications folder (inc contents), reformat the partition, (re)install the O/S, then copy Applications folder, and then start running applications, or do applications have to be individually reinstalled? Many thanks in advance for any answers to the above questions.