Yes, they can operate simultaneously in the same room since the 3Comm will be operating on the 2.4GHz band and the Airport on the 5GHz. band. Therefore they will not interfere with each other. I have a Linksys WRT300N and a Time Capsule set up that way sitting within an inch of each other with no problem.
See this link for whether you have to do anything to enable N on your intel Macs:
http://store.apple.com/us/product/D4141ZM/A