PowerPC noobie with questions..

yeah mate, on that box, id suggest office 2004... goes great, 2008 even runs like crud on osx intel..

no it is not caused by the hardware, mainly its just the laziness of developers to do universal versions of their software on offer now , but as you'd choosen a PPC Mac it is important for you to know they will perform the same way they did when they'd been new and there are still people out there developing software for the PPC Mac's running tiger

so i would not put leopard on it as it still cost a fair amount of cash , it kills performance
so leopard i would only put on a G4 under 1.5 ghz if i could not live without it for some strange reason ,
ok i love to play the old OS9 games and with leopard that is not possible as leopard doesn't offer classic support
even on my intel iMac i installed tiger,originally shipped with it just because of another feature called apple talk which apple forgot about in snow leopard

I have a 12" G4 PB 1.33ghz with 768meg RAM.

Runs Leopard fine.

The original 80Gb 5400 rpm HD died so I replaced it with a Western Digital 250Gb 7200rpm drive.

Still get 5-6 hours on the battery....

The additional RAM will certainly help. I installed Leopard on my old 1.33GHz G4 iBook after I gave it to my cousin, and it runs fine.

I agree with MacHam, that if you need Classic application support for old OS9 stuff, then yes, use Tiger. However, it doesn't sound like that is the case for you, and most newer applications that still support PPC require Leopard (for instance, Safari 5 or iTunes 10). If your girlfriend has an iPad or an iPhone 4, she'll definitely need Leopard in order to synch it to the computer.

You can install Safari 5, iTunes 10, Firefox 3.6, iLife '09 just fine. Office '08 is a mixed bag. You get some nice new features with it, but as VanneDC points out, Office 2004 is much more responsive. Thing is, '08 isn't just slow on PPC, it's been slow on Intel processors as well. The biggest problem was the 'bouncing icon' problem, where when you would try to open the program, the dock icon would bounce for a good 20-30 seconds before the program would ever fire up, which I observed both on PPC and Intel machines. That was fixed about a year ago, so it's better, but it's still a beast in terms of responsiveness. Stick with Office '04 if you can.

If you're going with Leopard, be a good partner and get your girlfriend a cheap Firewire-400 drive so she can run Time Machine...

yes as it needs to be ultra ata 100 and the original HDD was only a 4200rpm drive , so certainly if you can get 7200rpm that would boost performance , and as you already plan to upgrade the ram you need in the
2005 ! iBook 12" 1.33ghz which actually holds 1.5 gb ram , 512mb are on the logicboard already and 1 gb pc2700 200 pin sodimm is what you need in that model for under the keyboard in the user upgradable slot
instead of the earlier 2004 models which could only take 1.25 gb ram pc2100

i have a g4 ibook 1.2 with 512mb ram and it runs leopard fine. im planning on maxing out the ram just to do it but even if i dont, im happy with how it works on 512 mb.