Well, I learn something new every day, too.
For Windows XP, look up this registry key and see which version of vstudio the path is pointing to, if any:
If you have various versions of VideoStudio installed on Windows XP, and you have associated a file type to always open with VideoStudio, then you can tell which version is going to open by looking at that data for that key.
When I opened that key, X4's path was listed. I manually changed the path from X4's path to X5's path, and when I doubled-clicked on a file with a M2TS file extension (already had told Windows to always open that type of file with VideoStudio), X5 opened instead of X4.
So if a different version of VideoStudio opens than what you expected, then you should be able to fix it by editing the Registry. Warning: You are editing the Registry at your own risk. Your computer could malfunction and damage equipment and require re-installation of the operating system and applications. You have the wrong path name entered if VideoStudio doesn't show up in the "Open With" list, or if you browse to vstudio.exe, but it doesn't show up in that list.
Other applications, such as Audition, where I have 3 versions installed, don't have this problem because the executables were installed with different names. You can't change "vstudio.exe." to something else in other versions in order to get around the problem.
MotionStudio 3D 1.0; Corel VideoStudio Pro 188.8.131.52 (Ultimate)(Discs), Corel PaintShop Pro 184.108.40.206 (Download)