You said Powerbook or Emac. Very different computers - one is portable. You first need to decide if you want a desktop or laptop. We can then help you decide better.
Also, list the kinds of apps you will be using or things you want to do (Word, photoshop, dvd burning, movie editing, etc.)
Your price limit gets you a 12 inch Powerbook. That same price ceiling gets you a 17 inch emac, RAM from an outside vendor, and an iPod. Portables are more expensive - look closely at what you need.
Of those who brought computers to college in 1999, 20-30% of NEW students brought laptops. In 2003, that number was above 85%. Laptops have closed the performance gap a lot in that time -but in the end - it depends on what you need and on the funds available to do it.