If you have the money to buy a 1GB or so Memory Stick Duo then get the PSP if not... Well you can forget about listening Music in a PSP,
Because you need the memory to save those game saves, and there will not be enough space for music, unless you are ok with hearing the same 15 mp3 over and over again!
Its 15 - 25 mp3 in the PSP against the 7,000+ in the Ipod....
