The problem with the transponder is that it will have to be programmed. And from what I understand, you can do it one of two ways:
1. If you have two keys already programmed there is a way for the 3rd key to learn the code (this is something you can do).
2. You can take it up the butt by taking it to a dealership or key place and paying a lot of money (here it cost about $125)
There is a 3rd option. You can do the viper key mod by buying a viper key from a vendor or ebay. Then cut you existing key up and get the transponder out and superglue it to the inside of the steering column. This way it will be close enough to work when you put your viper key in the ignition.
I am in the same boat as you. I think that I would like to have a normal set of keys and do the viper key mod both.
There are instructions somewhere around here for the viper key mod.