Okay, news - and good ones indeed:

"Legendary 727" does not have any issues with Vista. Actually (I would say) that "727" just needs the FS2004 to run. And there is absolutely no problem to run FS2004 on Vista.

I installed and activated it online this morning and everything went smoothly (not so much with "Legendary 104" which I tried to install afterwards - see my post in the respective department). As posted yesterday, I "just" had to shut down the firewall to activate "online" rightaway.

I can tell you, it's big fun to see and fly that jet in FS2004! (I began with low realism to get started, but then performed my "maiden flight" from Hamburg to Berlin - plain cool.)
I (of course) "just" need to learn about the tids and bits - I was missing that lady on the co-pilot's seat for example, or I would have liked to switch the voices from British English to American instead (as I was flying under PanAm colors). But I hope, I will find out about things like those soon...

So if you are still interested (guess you should be back from Miami meanwhile): no problems to run "727" with your setup. Go ahead!