Vista 64 has one or two issues with FSX. We can't guarantee compatibility but if the problems are not too horrendous, we will look at it for an update/patch. Best I can do at the moment.
Please remember that Wilco has an excellent approach to development. A download release is made available first, which carries a full programme of updates and bug fixes. This helps us devs to iron out problems, put in any wishlist items people may have made and so on, before the boxed product is finally manufactured. So, no download purchaser ever has less than the final boxed product, except the printed manuals and a shiny box.
WIth P180II (despite what some people may say :>)) it is a complex build and has input from several quarters such as avionics and gauge programming which is a different team to say, the modeling. So to get things right is a bit of a balancing act initially but it all comes right in the end.