First off, you will want to head on over to http://forums.gentoo.org/ and post your questions there. There is a great Gentoo community just itchy to help you. :)
"I would call myself a relative newbie do building kde and gnome would seem a daunting task."
To install KDE you simply type: emerge kde
To install Gnome you type: emerge gnome
Gentoo's portage will automagically grab XFree86 and all of the other dependencies for you! It really is that easy. You will, of course, have to configure X once the install is complete. There is a Desktop Guide on the Gentoo website that is chock full of help.
"i've just completed grabbing the basic livecd iso. I'm not sure what is actually on the stage 2 & 3 archives, but I can cheat a little on those as a friend does have a cable modem and an LS-120 drive, which will enable me to grab those files."
You will want to install from stage 3. A stage 3 install requires much less downloading. All 3 stages are easy though (especially if you print out the documentation ahead of time). Basically, a stage 3 install has pre-compiled binaries so your machines performance might not be as good as a stage 1 install, BUT you can always re-emerge any apps once you've finished installing (to get the benefits of a customed compiled app).