i'd say the PBs are what you should be looking at, as others have noted. don't buy RAM from apple. use dealram or ramseeker to get 256-512MB modules, and newegg
for a 1GB stick. others might have workable suggestions as well.
the faster HDs in the PBs will be beneficial for anything video or audio intensive. my iBook has handled anything i've thrown at it, but then again i did stick a 7200rpm drive in my system.
also, make sure to calculate how much an educational discount will cost w/ taxes included, vs. , for instance, a machine from amazon that u will get w/ a ~$150 rebate, free shipping, and possibly no taxes depending on where u live. the rebate deals can often beat out the apple edu discounts when u add it all up.
hope this helps.