I just purchased a new Core i7 computer to speed up my HDV video editing, encoding and rendering as well as a Prospect HD 3 upgrade (from Aspect HD) license. I am currently happy and using Premiere Pro CS3 with Aspect HD and I am intending to use that workflow on my new super computer until Prospect HD ver. 4 comes out. But I also want to install Premiere Pro CS4 and the current Prospect HD version on that same computer and see how it works. Can Aspect HD and Prospect HD co-exist on one pc if one is used with CS3 and the other with CS4?

My understanding is that you should NOT have more than one Cineform product installed on a computer at once. Possible exception if you are running dual boot on separate partitions/installations.

Aspect HD and Prospect HD have a huge amount of common components and installing both will only cause pain.