itunes library from wav to aac?

[ntscan]

I imported all my music into the itunes library as wav files so that I can listen to them over my main system....but now I want to convert them all to compressed files so that I can load then up on my new 4th gen 40gb ipod....I fried the 3G version with wav files....the 32mb buffer isn't enough so the puny HD is constantly spinning and it just couldn't take it....plus the battery life is cut in half...apple really shouldn't advertise the fact that is takes wav and aiff unless they drastically increase the size of the ram.....