Highest system is Tiger 10.4.11. I would recommend maxing the memory for that. Ralph

you can get away with Lepoard but not Snow Lepoard due to no PPC support

If you have tiger laying around, use this if you cannot afford upgrades for it, otherwise leopard may not run well on it

The maximum OS you can run is Leopard (10.5.8), however I recommend running Tiger (10.4.11), because Leopard would be a real drag and incredibly slow, with bad performance.

I would also suggest maxing out the RAM, which you can do at 1152MB, however due to slot configuration, the best you can do is settle at 1.0 GB (1000 or 1024 MB), you could put something in the other slot, but it would not be detected, you can get this stick here.

As for the OS, you can get it pretty easily on eBay or Amazon, such as right here, however if you google around there are plenty of Macintosh sites and sellers that have whole archives of every install Disk and will sell to you for a good price.

I have book...upgraded ram from 256 to 1.gig of ram...replace the original 40'

hd to a 160..and jumped it from Tiger..to Leopard..10.5.8

runs much better...than it ever did...and for a powerbook that's 8 yrs old,

that's great..and it still turns heads...

I once had a PowerBook Titanium 867 with 1 gig RAM and it ran beatifully with Leopard.

According to Apple-history.com. the max is OSX 10.5.8

If you have a slow PowerBook, I suggest you use OS X 10.4.11, as it is the fastest with older mac's. If your mac has more than 2 gb of ram, then it is probaly OK to upgrade. If you are simply upgrading to get a better dock and theme, you should get ShapeShifter and ClearDock at: http://shapeshifter.en.softonic.com/mac or http://unsanity.com/haxies/shapeshifter