The PowerBooks use ATA hard drives, not SATA. Either 5400 or 7200 rpm will work. The 5400 rpm models will generally be cheaper, run cooler and use less battery power. The 7200 rpm models would give you marginally better performance. Check out the ifixit guide to be sure you feel comfortable with doing the upgrade yourself, or find a Mac certified tech to do it for you.
BTW, how much RAM do you have? If your RAM is limited, you may want to max the RAM first, which usually gives more performance boost than increasing the hard drive speed.