Yo, Cheese try this as a rough guide for your drive.
/ partition - 300MB should easily be enough.
/var - if you are going to run an ftp server then keep var in a separate partition as if things go pear shaped the logs generated will expand and cripple your system if they fill your /usr partition.2GB
/home - normally this wouldn't be a slarge but if you have all those files and they must be on your hard drive then this is going to be huge (25GB?).
/usr - I would go for about 10GB
swap=same as your RAM
Really though I would consider putting all those mp3 files on your other drive and hosting both windows and linux on the main drive - say 10GB for windows and the 30GB divided up for linux.
Anyway,that's only my ideas but I'm sure you will get more suggestions soon.
Good Luck