Q: PowerBook G4 in 2014

Powerbook G4s are quite capable when it comes to the internet, even word processing, spreadsheets, and some older games depending on what you want to put into it.

500 Mhz to 800 Mhz models can go up to Mac OS X 10.4.11.

867 Mhz and higher (1 Ghz is higher) can go to Mac OS X 10.5.8, but eliminate the Mac OS 9 application compatibility when taken to that level.    There is though this tip on dual booting Mac OS 9 and Mac OS X 10.5.8 which is possible on some models:

https://discussions.apple.com/docs/DOC-1757

This thread deals with how to get the latest Flash browsing on your Mac:

https://discussions.apple.com/thread/4781929

This tip explains Java:

https://discussions.apple.com/docs/DOC-6491

Most Javascript will operate fine.

No Silverlight based video such as Netflix will work.

If you have data on it that you eventually want to migrate to an Intel Mac, use this tip:

https://discussions.apple.com/docs/DOC-2295

Lastly if you don't have the original installer discs, you'll want to identify the age of the Mac:

http://support.apple.com/kb/ht3065

https://discussions.apple.com/docs/DOC-6413

This will help you know the minimum retail operating system you can install.

I would not install anything earlier than Mac OS X 10.2 when it comes to Mac OS X.

Tips on upgrading older Macs than 10.2, begin here:

https://discussions.apple.com/docs/DOC-2125

OK, that's a Classic only Mac OS 9 machine.  If you don't use Mac OS 9, you may want to see if you can find 10.5, 10.5.1, 10.5.4, or 10.5.6 retail:

https://discussions.apple.com/docs/DOC-2275

For the best internet support.

And apply the 10.5.8 combo update so you can get the latest Java for 10.5.