My mother asked me a technical computer question that I cannot answer (surprise, surprise)- but I told her "I know where I can find out..." Don't let me down, guys!

Mom has a Yamaha PSR 510 keyboard and a Tangerine iMac (yecchhh - like Macs, hate the new "plastic fruit" look). She would like to hook them together to use a software package to learn how to play piano (after making US take lessons because she never had a chance to...). She needs to buy an additional USB port hub, because the two on her iMAC are filled by the printer and keyboard (computer, that is). She also needs to buy a MIDI interface of some sort that is compatible with her keyboard (I don't know if MIDI formats were standardized by the time Yamaha made that particular model - I know our PSR 500M isn't). What recommendations do y'all have, and where can a retired lady in Minnesota buy them?

Thanks!