I am trying to put KDE 2.0 as my desktop environment, but I cannot seem to find where I can download it (tar file maybe?). This is for ubuntu. If you know how to do it for gentoo as well, that would be awesome, but my main concern is for ubuntu. Thanks!

No idea about 2.0, but you can download 2.2 here:
http://download.kde.org/Attic/2.2.2/src/

You'll have to compile it yourself though, and I cannot give you further instructions for that...
But there's of course no difference whether you do this on Ubuntu or on Gentoo.

Just to be sure about what we're talking: KDE 2.0 was released October 2000 and used Qt 2.0
You'll likely also have trouble compiling either w/ gcc > 2.95

Would I be able to compile kde 2.2?

With an older gcc + glibc, sure.

But are you trying to do?
If you just want to make KDE 2.x screenshots or similar, "ancient" knoppix version (<2.2?) might still boot (at least in a virtual machine)