pacific fighters standalone works perfectly. so does forgotten battles even with ace expansion pack installed. but when i merge it with pacific fighters it doesn't even start up anymore.
any suggestions?

I don't think that there are many of us still using versions of IL-2 earlier then the '46 one, so you might have trouble finding a definative answer to that. If at all possible I'd look at getting '46, people run that under Vista with little problem. You should be able to get an IL-2 '46 DVD for about $20 or so, and you will get many new planes, including jets etc. There is even a new patch out (4.09m) with a few more (you need to patch to 4.08 first, before installing this patch)

One thing to ensure when running IL-2 under Vista is that you do not install it in the default location (usually C:/Program Files), as this leads to problems - create another folder instead.

thanks for the fast and helpful response. so that means that with 1946 i don't need the stack of cds (fb+aep+pf) anymore? i thought it was just another add-on...

Il-2 '46 incorporates all the aircraft etc from the previous CDs, making installing much simpler.

It may be possible to download it using Steam, but the DVD install seems to give the least difficulty - you do need a DVD reader of course.