First off, make sure you've calibrated the battery. Let it run down until the PB turns itself off and then recharge it - full instructions in your manual.
When it's on battery power, turn off airport and bluetooth if you don't need them. Take it down a few brightness points (F1) and make sure that your Energy Saver settings are on 'Longest Battery Life' in the system preferences. Shut down programs that you aren't using and you'll get longer too.
I get about 2hr 30 on my year old 15" with Airport on
And another tip, rather than a vague thread name, it's worthwhile relating it to the question (ie Help with extending Powerbook battery". You'll get help faster.