You can download Mandrake here:
http://www.linuxiso.org/
As far as a distro to start out with, Mandrake is a good one in my opinion.
If you haven't, I highly suggest you sift through these threads as well - especially the first one:
<a href="http://tfproject.org/tfp/showthread.php?s=&threadid=4170">ATTENTION: 'Why Linux is Not for You: The Lengthy Rebuttal of a Linux User'</a>
<a href="http://tfproject.org/tfp/showthread.php?s=&threadid=199">Which flavor of Linux?</a>
<a href="http://tfproject.org/tfp/showthread.php?s=&threadid=203">Top Linux Downloads</a>
<a href="http://tfproject.org/tfp/showthread.php?s=&threadid=144">Linux software equivalents</a>
Linux is VERY different from Windows and Mac OS. Different distros leave various amounts of things to the end user to do, but one thing that can be consistantly said across the different distros is that they all generally require the user to pay FAR more attention to details and the inner workings of the OS than Windows or Mac OS.