For a dually board, you are going to need 2 CPU's for it to function. As for overclocking, the K7D will overclock, just not to the extent of an nForce2 board. One problem you may run into is that this board has been discontinued, so trying to find a new board will be a challenge.
For a single CPU system, you might want to check out the MSI K7N2 Delta-L @ Newegg for $73. This is the only Red nForce2 board that I could find. I'm not sure of its overclocking potential, but I do know that people have had problems with it.
If you can possibly go with an Orange board (it's almost Red ), then the NF7 is the board for you.
All of the NF7-S Rev2.0 boards should be red (well its more of a dark orange.) The MSI K7d - Master - L board will allow you to overclock but your limited by the FSB, you can only raise it up to 150FSB. After this you have to pin-mod the processors to raise multipliers to go further.
You might want to check htis thread as Majormav took the Duallie to new Xtremes HERE