Casablanca Car

I am finishing our unfinished basement in our new house. There currently are 2 vents in the duct work currently, but I am building a spare room and what it ventilated too to provide ventilation (heat/air). Since we are installing a drop ceiling, I was thinking of tapping into the current duct work and running a pipe into the new room and vent it through the drop celing. Here are my questions:

1) Can this be done without compromising current flow to my upstairs?
2) Where can I find a vent for a square panel drop ceiling? I can't find one online.
3) Do I need to install a blow, since where I will tapping into the duct work (~6" hole in top) is at the very end of the duct work run.

Any and all tips would be appreciated. My wife doesn't want to just install a plug in heater in this room. She wants a vent off of the current run of duct that we have down there.