here's the deal that i can figure out so far with iTunes. If you own the CD, you can then choose the preferences of how you want to download your songs from the cd onto your computer (mp3, aiff, acc, etc... and at what rate, 128, 192, lossless, etc...) But if you buy songs from iTunes, they are 128kbps ACC files. Yes this sucks. the only silver lining is that ACC is a better compression type and 128 sound about the same quality as a 164, or even 192 mp3(so they say) It does sound better than 128 bit mp3, but not sure if it's as good as a 192 mp3.
Anyway, I haven't found a way to choose the format of the download you buy from iTunes, which is kinda lame.