Hi Bitflipper,
I had a similar problem and did the registry edit myself with two programs that weren't showing up on the VST plugins list:
Beatscape and z3ta+
and Dimension Pro was reporting back to me that it wasn't properly installed. I found that despite the fact that I have adminstrative rights on my Windows XP computer, I had to log in as "Administrator" in order for these programs to install and work correctly (even with the registry hack for the z3ta+, I still had to run Sonar as an Administrator for the synth to play from the rack once it appeared!).
I have now set up an administrator account and run all my Sonar related software there instead (even my project 5 installation was asking me to reinstall from the original CD!!)
I don't know when my security permissions changed on my system (I'm the only one who uses it, so suspect some foul play from the internet!) but it caused the same symptoms as the ones you described for z3ta+.
Hope this is of some help
Uche :)