Hey Alfiean, and welcome to the eForum!
Shame to see you've joined us under such circustances, but we'll do our best to help out based on the fantastically detailed post you've provided above.
Before we start though, I will say that we're not Microsoft Training Accredited, so any PC-specific suggestions made delving deeper into Window's underbelly will be out of experience, and should be followed at your own risk. This isn't to say we bumble through information, but just to backup in case something goes wrong as we're not legally liable.
From what you've said, my initial reaction is that Vista is making real mess out of VMC 9.3.6... can you try uninstalling it and loading an earlier version? Check out our
VMC Drivers page, perhaps maybe start with 9.3.3? We keep these publically available because we know that they can resolve some compatibility issues.
Other than this, have you tried assigning it another port value? This can be done from Device Manager, by right clicking the modem entries and assigning an alternate virtual port number. There may be a conflict in progress
Let us know how you get on! I'm sure one of the community will drop by to lend their expertise soon, too.
Daz
eForum Team