OK, well my suggestion is to go ahead and partition the 30 GB drive... 10 should be more than enough for unix, especially if you're basically just playing around with it.

Depending on the version/distribution of Unix or Linux that you end up obtaining, installation should be fairly simple. Most have the type of hand-holding that you've come to expect with Windows now.

Just boot from the cdrom and install to the new partition, probably hda1 or hda2... depending on any other partitions you may have.

Check into the site I gave you before. That should have a tutorial on it.