Hopefully you made a backup first.
Unfortunately, Tanzanite does not have any 3g or GPS coverage. In the simplest terms I can explain it, Tanzanite was an attempt at making a full AOSP ROM (completely free of anything Moto), but the fallback to that is that some moto files are needed to make certain services work (ie - 3g and GPS). This is why none of the crucial services are working.
As far as ROM manager goes, im not familiar with the app as I use Koush's Bootstrap to get into clockwork recovery myself. Someone more familiar with ROM manager may be able to help you with this.
Basically there are two good options here. You could use ROM manager to boot into recovery and flash a backup if you made one, or you could do an SBF using RSD lite. There is a third option which I wouldn't recommend, and that would be downloading another ROM such as Liberty or Fission and flashing that.
There are a couple stickies at the top of the "Droid 2 Hacks" section of this forum that will give you some insight on how to sbf your phone (Specifically the Droid 2 Hacking/ROM install class), which would most likely be the best option.
I will say that Im not an expert by any means, but this is the best solution I could offer you. Im sure someone with a little more experience will probably chime in on this.
Lesson learned though, always do your research before flashing anything =) Don't panic though, one way or another, we'll help you get your phone straightened out
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