Hot Air Ballon!

[Xgkkp]

I don't know anything about editing fs (yet)

But I suppose you could treat it like a helicopter for the vertical stuff, though I'm not quite sure what you'd do about the horizontal / making it drift with the wind....

It would be kinda cool I think...

[ChuckMajik]

There already is a hot air balloon for FS.
I believe it was uploaded to flightsim dot com awhile ago.

[Travis]

There are several, my favorite being the "I Love NY".  They can all be found here somewhere.  Try the Misc section of FS2002.