There are 3 cheap UNIX-type systems that you can run on a PC:
1. Linux, available in many distributions. SuSE and Mandrake are the most polished for newbies, and both work well with Windows on the same computer (even on the same disk). Linux costs $40 retail or free (Mandrake, not SuSE) if you want to download 3 or so 600MB disk images and burn your own CDs.
2. FreeBSD, also available for $40 retail, and also downloadable for free. Much more difficult to install for a beginner than Mandrake or SuSE Linux.
3. Sun Solaris, also $40 or $20 if you download CD images. Paying the $20 is actually a good deal, because their server is available and it's easy to access. (Getting access to a server with the Linux CD images could take days.) Extremely difficult to install in my opinion. I have 30+ years of UNIX experience, and have installed Red Hat, Mandrake, SuSE, Lycoris, and FreeBSD, but I am now on my 6th attempt at installing Solaris.
4. For more tips, see my article at
www.basepath.com/linux.
5. Easiest route: Buy the SuSE or Mandrake retail packages from CompuUSA or Best Buy. You get some docs and don't have to worry about downloading and burning CDs.