I am finishing my basement and want to add heat registers. The furnace is in the basement with the duct work overhead. I want to put registers near the exterior walls in the basement ceiling. Can I cut registers into the same ducts that take the heat upstairs or will this take away too much air flow upstairs?

It will take away from the upstairs. The registers have dampers on them that you can adjust to help decide how much air you want. You will also need a return air in that area. Its hard to heat a area if you can't remove the cold air.

Adding another area to your heating equipment are you sure the furnace is going to be big enough

I am finishing my basement and want to add heat registers. The furnace is in the basement with the duct work overhead. I want to put registers near the exterior walls in the basement ceiling. Can I cut registers into the same ducts that take the heat upstairs or will this take away to much air flow upstairs?
You can do this but it will take away some of the cfms (air flow)from the main supply trunk how much depends on the stattic pressue of the blower. You can you can change the blower(indoor fan) speed to a higher setting just by changing the dip switches on the board if you hve a varable speed fan if not simply change a wire from medium speed to high speed or low to medium