Linux is basically a PC version of UNIX. There are MANY variations of Linux to choose from, but the best ones that I know of are Red Hat, Mandrake, Suse, and Caldera.
It would probably do you alot of good to get a copy of one of these (I'd suggest eBay...you can get a copy of the new version of Red Hat Linux (7.2) for around $5 +shipping from various people on there). Also, a decent book on Red Hat Linux will run you about $40 or less. Just look for any book that refers heavily to Command Line
You'll learn alot of what you'll need for UNIX that way.
Also, I don't think I'd try dual-booting if you're a Linux/UNIX beginner....Lilo does NOT like FAT partitions (I learned that the hard way recently). Just get an old PC from somewhere (atleast a low-end p-ii like a 266mhz, and at least 32-64 megs of RAM) with a decent sized hard drive so you have some space to work with...maybe around 5 gig or more.
Anyway, something like that should be able to get you going. Plus, if you've got 2 PCs to work with, you'll be able to play around with networking them together.