I have an interesting problem which could be related to the "it doesn't work" comment.
I've recently gone FS9 (following a HD corruption), from a very stable and well customised FS2002 setup (FSUIPC 3.47).
So, I'm now running FS9.1 with FSUIPC 3.51 (registered), and I've noticed that with wind smoothing switched on, aircraft like the PSS Airbus (which used to be well behaved in FS2002) don't correct for the wind properly in FS9 - the aircraft weathervanes into the wind, and slowly drifts off course, in an upwind direction (relative to the crosswind component of the reported wind).
When the aircraft comes within about 3 miles of the next (flyby) waypoint, it pulls this very hairy "S-turn" across the fix, before heading to the next fix, slowly drifting off course again. Rinse, lather, repeat!
This applies whether I'm flying offline with FS9 downloaded weather, or online with VATSIM (Squawkbox 3) weather. No ASV or any other WX addon.
As soon as I switch the wind smoothing off, the aircraft becomes true to the the route being commanded by the autopilot - but of course, back to the very wild changes in the winds aloft while in the cruise. (Which seem amplified with SB3 WX!)
Becuase of the recent system rebuild, the last FSUIPC I have is 3.47 (so I've not been able to "back out" a point release, back to 3.50, like some others tried).
Pete, if there's anything you need in terms of logging or want me to try out, please let me know.
Thanks!
Mike