Kabudokan has it right on but there is another way. You need to make an aux bus (go to file-properties-audio and increase the # of stereo busses)then assign the track to a buss. you can put effects on the bus. Think of this as a channel or buss insert on a mixing board. This would be the best way to do it for EQ's and compression. You can also assign an effects bus. (Right click over the mixer section, select "insert assignable FX" you will then have an effects send) with is better for reverbs and other FX. you will then need to assign the FX send to a buss. Sometimes I create a buss just for this, or sent it back to a particular channel (buss). The Vegas Pro mixer is pretty much not well designed (there is no Master fader) but overall it's a very nice program as far as the ease of mixing.
-jhe