Congrats! I trained for a couple of triathlons with TNT (LA) a few years ago. They really are geared to train people who have little or no experience with a sport, and to give them everything they need to get ready.
The best people to talk to about your training concerns would be your TNT coaches. They will likely have different groups - faster riders, slower riders - and lots of good tips on keeping up with the program. And, as you point out, your real commitment is not until January. You should know by then if you are feeling up to the challenge. In the meantime, go to the workouts, follow the training plan that they give you, and have fun!
Now, Solvang is a hilly, tough ride, to be sure. I rode the half this year and will ride the full in 2011. It is also packed with Team In Training groups, which will make it a super fun ride for you!
Finally, fundraising...$2500? If you can find a)25 people to give you $100 or b) 100 people to give you $25, you are there.
Go Team!