I have been writing software, and developing microcontrollers, since the earliest days of microprocessors, and I spend way too much of my time fixing IT issues, so we will have to agree to disagree on this one
I've just done a quick count and have about 130 apps on my winXP PC, and they all work. I know for a fact that a load of them, including the most valuable ones, won't run under win7.
I even have an old LOOX PDA running the crappiest and buggiest O/S ever made (WM), so why do I keep it? Because it runs TomTom6, which a good friend gave me for my 50th birthday, which does all I need for car nav, and it runs it well.
In the meantime, the OP has a bit of software which runs under XP but not under win7, so what solution do you propose? I don't think sending a link to this thread to Garmin, with a note to improve their software quality, is going to be productive.