A friend who uses Edius showed me a video he produced in which he selected a single color (red roses) which were displayed in full color. All other colors were displayed in black and white. Is there a technique / filter that can be used in Vegas Pro 8 to accomplish this?

Yes.

The secondary color corrector can be used to create this effect.

Volume 2 #10 of Edward Troxel's excellent newsletters (http://jetdv.com) has a short tutorial on this.

Although written for an earlier version of Vegas, the technique works just the same in V8 Pro, the secondary color corrector hasn't changed.