Windows to Unix

burn the image to CD or DVD.

Boot from the CD, follow the installation instructions. You can either install right over Vista, or both operating systems can share the drive(if large enough) in a dual boot configuration.

Another option: Download and burn a Linux Live CD image, you can just boot from that CD and use Linux without installing anything.

A third option: Install the VMWare player, and download various Linux VMWare images- this essentially runs a virtualized operating system within you Vista OS just like a program.

Ubuntu is a very popular Linux distro, especially for the inexperienced. PC Linux OS is also a good starter distro. Of course, you can download as many as you like and try them all.

http://distrowatch.com/
A place to check out most all Linux distros.
Just follow the links.
(Make sure you get a Live CD if that is what you want. If you want installation CDs, make sure you get those. Just recognize the difference.)
http://www.livecdlist.com/
A list of Live CDs only.

http://vmware.com/products/player/
http://vmware.com/appliances/directory/cat/45
VMWare Player and appliances links.