Everything I have tried has been ugly.

I want to upgrade gnome to the latest version (Like in Ubuntu 9.04) a couple of nice features have caught my eye there, not to mention nm-applet and Evolution.

Well I went and used the testing repositories and a whole host of programs wanted to uninstall themselves. I commented out the testing repo's and updated to cancel that operation out.

I then tried

As suggested in farslayer, well my experience was less than lack luster. As a matter of fact it stunk.

So my question; is there a way to cleanly update my machine to testing without doing a clean testing install?

Not really - if your setup is now crud, then even changing the repo(s) to testing, will not tidy it up much.
A clean install is probably better, if somewhat a PiTA.

I don't know, but maybe you could try a safe-upgrade first, and then try installing apt, and then try the full-upgrade. That was the recommendation for upgrades from Etch to Lenny, so it may work with Lenny to Squeeze.

If your using kde then yes a lot of packages will be removed moving from stable to testing. stable has kde3.5 while testing has kde4.

Another thought: If from your previous attempt, there are still issues that aptitude is trying to resolve, then it may be an idea to open the ncurses console window of aptitude, press Actions with the mouse (or press Ctrl-T with the keyboard), and select "Cancel Pending Actions". Close the ncurses console window of aptitude, then update, and try safe-upgrade, followed by install apt, followed by full-upgrade.