Been tinkering myself for about a month now. Built myself a Linux box out of a mixture of spare and new components.
I bought a book on Ubuntu that came with a distribution CD-ROM in the back (Ubuntu 9.07), which I installed then upgraded to 9.10. You can also download a fresh copy of 9.10 from the Ubuntu website, but a reference book is always a good idea when starting out with a new OS.
I also tried SuSE, which I didn't like, and OpenSolaris from Sun Microsystems. OpenSolaris is basically a free version of Sun's Solaris version of classic UNIX, and, IMHO is aimed more at the large scale professional / business application than Ubuntu.
Ubuntu makes it very easy to set up, especially peripherals like printers and internet / network connections (I have mine connected to a DSL router that also hooks up my desktop Windows PC, my notebook and my netbook). Solaris, on the other hand, isn't too "idiot friendly" in this respect.
Other notable mentions include RedHat, which I haven't tried, but which has been around for quite a while.
There's a whole host of software out there, and you pretty much don't need any Microsoft products at all. OpenOffice 3.1 is pretty much on a par with Office2003, certainly in terms of look and feel, probably in terms of functionality. It's likely that only very specialist programs (finite element, CAD, etc.) or utilities for specific digitalcameras, all-in-one printer/scanner/copier, etc. will be the only "weak" areas in Linux.
Give it a whirl, but be prepared to still need Windows for some apps for the foreseeable future.
I should be sponsored by Cyrus and Chord (and B&Q)!!