making mp3's from aiff's

[John Reed]

I'm trying to make some mp3's of various specs from aiff files to put a 
band's music onto their website so it can be downloaded in various 
resolutions according to the user's connection speed and machine...also 
it needs to be playable on a windows machine or a mac...
I haven't found an application yet which gives me choices about 
specifications - itunes gives me a 46mb mp3 which is too big, final cut 
pro doesn't give me an mp3 export option, or quicktime, or peak dv, or 
soundtrack (as far as i can see anyway)

any clues?
thanks in advance

john