you definately want to partition it. i currently have 15 gig in my linux box broken up in the following way:
300 Mg /
10 Gb /home
400 Mg /mail
300 Mg /root
350 Mg /tmp
3.65 Gb /usr
these numbers might be off a little, i am not at the machine right now so this is all off the top of my head. you might not need a separate partition for mail, but this should give you an idea.