as i have one already and have an i tunes account on this computer etc, however my dads on about getting one but this is the only computer, can we both run seperate ipods off the same computer? or would both end up with the same tracks on them etc?? and also would it matter if ones a 4gb nano and the others an 8gb nano??

you can easily run 2 ipods off one computer. The easist way of doing it is to create different playlists. then when syncing your ipod on sync with the playlist with your music.

If you're using separate user accounts on the computer to start with then just running iTunes will give you your own installations. If you're just using one account on the computer then you can still run multiple iPods off one iTunes library by syncing each iPod to different playlists or combinations of playlists, you can even have different iTunes store accounts but would have to keep switching and each person would have access to whatever the other paid for.