Hi melrowgo, there are no significant differences between a rooted Nook Tablet and a rooted Nook Color. Both allow root access to the underlying Android which means they can both be customized and allow access to apps outside of the B&N market.
At the moment the NC has an auto/manual-nooter script which allows some useful tools to be installed on the NC as part of the rooting process as well as having custom kernels and ROMs available. You can also install these app tools on the NT manually once rooted it just doesn't automatically happen as part of the rooting process (for the moment at least) and the kernels and ROMs will have to be developed.
The real difference between the two devices is hardware. The NT is much faster and includes a mic which the NC is lacking. As far as what you can do with a rooted NC and a rooted NT it will eventually be the same as more work is done by the devs for the NT.
With a mike you can sign up for google voice to get a phone number then download GrooveIP and now you can make free phone calls...at least in theory since i do that on my galaxy tab wifi
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