as far as distros go, you can find as many people praising one as the other, I use Mandrake, if for no other reason than that's the one I've got....... I've installed (in the past) Slack, Caldera, Redhat, Debian...... the list goes on. I like Mandrake for it's ease of install, and it's ability to resize an NTFS partition (which your Win2k probably resides on) during the install. For your install.... set up Linux first, doing a "custom partition" during the install and leave yourself some empty, unpartitioned space on the new HD for windows. After the install, go ahead and use something like "Ghost" to copy your existing windows partition onto the new hard drive. I seem to remember that WD hard drives come with a small utilities disk that may be able to do this for you.. Since you have a huge hard drive, and I assume you won't be running a server, give yourself about 80GB for windows, and 80 for linux.... you shouldn't run out of space anytime soon
also.... swap space, be sure to allow some (about twice the space as you have RAM) ie: if you've got 512MB of ram, make a 1GB swap partition on the new drive. Adjust these sizes as you see fit for the "third partition " in the middle ( I guess for shared files.) For the apps...... almost anything available for Windows has a clone available for Linux, just search around (
http://linux.tucows.com) is a great source for linux apps.
Hope this helps
Smee