Key plug in for Vegas?
 

There is a very cool plug in for FCP call PHYX Keyer. I've just seen a poorly lit green screen interview rescued by PHYX by taking precise control of the green-grey color and replacing it with a proper green. Is there anything like this for Vegas?

It is a little harder to get a good chromakey out of vegas - other keying software has the specific functions in an easy-to-understand interface. With Vegas, you end up with quite a chain of filters if the original shot wasn't perfect.

The particular function of green replacement before cutting the key can be done with the secondary color corrector and perhaps chromablur. Keith Kolbo has a couple tutorials out there, if you search for them.

Attached is an example. The first step is to "select effect range", then "show the mask" and tweak it, using the bottom set of controls, then un-"show the mask", select a color with the wheel that you want to be the new replacement, and bring up the saturation.