That's a plenty big hard drive for any regular user. I'd set it up as a 120/40 with the 40 for data files. You could purchase something like Partition Magic so that you can partition your hard drive without having to FDISK or reinstall.
Or you can just buy a uber-cheap 40GB hard drive and make that the slave and use that for backing up DATA. Of course, it being a hard drive, you also want to back up to CDROM media or DVD-R media if you have a bottomless wallet.
