I'd suggest the one-and-only (new edition) of _Linux For Dummies_, which is definitely written from a "switcher's" perspective, and it usually comes with a distro already on CD; and once you're done with that one, I'd go to the library and haul out every relatively new book on Linux they've got, and read as far as you can until you're confused. That is, read _L4D_ (well, the opening chapters anyway) *before* you install, and then go from there.
If you want to just *try* before you buy, you can also get a distro called Knoppix (it's a Mandrake variant, IIRC), which comes self-contained on its own CD-ROM. Insert the CD, reboot your computer, and presto! Instant Linux machine, no messy installation required! Granted, it's mostly read-only because it's intended as a demo, but it does enough that you can learn the file system, see the interfaces and the software, and get an idea of what you're getting into before you start 'fsck'ing around with fdisk and repartitioning your hard drive, or anything permanent like that. Then, once you're done, shut down your computer, take out the CD-ROM, and reboot. Behold your Windoze box returned like magic!
Some other good websites are:
http://www.techtv.com/screensavers/answerstips/story/0,24330,2570014,00.htmlLinux for Windows Users
http://www.linux.ie/newusers/beginners-linux-guide/Beginners' Linux Guide
http://beginnerslinux.org/index3e.htmlA series of PDFs downloadable on various topics you'll need to know to get started
http://dir.yahoo.com/Computers_and_Internet/Software/Operating_Systems/UNIX/Linux/For_Beginners/Yahoo's beginner Linux links
I also have some more information I got from a friend some time ago that I could send you, if you PM me, if you're really interested. While I'm not using it right now, I was using it almost exclusively about 2 years ago, and learned all the programming I know on it.
Edited for clarity, to make what I had left for inference plain by explanation. Bad tech writer, no paycheque! (No fscking paycheque anyway, goddammit!)