I started to running into problems a while back. I only had the 1 workstation and I was trying to decide between NLE's. I had VEGAS, Premiere, MediaStudioPro, and Xpress DV installed on the same machine. Along with PhotoShop, Illustrator, Cleaner, and AfterEffects. I started to running into problems after a while. Maybe it was because I was installing/uninstalling different plug-ins and FX to try them out. I had problems with the programs choosing Codecs and such. I also noticed that sometimes when I would change a setting in one NLE it would affect settings in other NLE's.
I wouldn't do it again... but I anxiously await your findings. Also, may I ask why you would want to install both of these NLE's? Do you intend on using each for a different purpose or just to try them out? VEGAS is as close to REALTIME as you will get. Xpress DV annoys me. It takes up too much system resources and does not cooperate with my work flow. Xpress DV was intended to be put on it's own system with no other NLE. Just like it's big brother and sister. Composer & Symphony.