Not sure what to say on this one. For the most part the vegastrike engine (which is what gemini gold is based on) is not very chummy with 64 bit windows. Its an ongoing issue that hasn't been nailed down yet. A lot of the crashes on the 32bit side I have not been able to reproduce.
As for 64bit.. I'm still working on getting a 64bit exe ready for release. I am hoping that John can help get gemini gold running off the latest vegastrike code so we can keep this game up to date.
If you don't mind some non cannon items you can try Privateer Parallel Universe ( http://pu.wcjunction.com/
) the code is a little more updated but also hasn't been worked on in awhile as its project admin has a lot of RL issues to deal with at the moment. If you try PU and still have issues post over on the vegastrike forums and we will see if we can't get some working for you (if no one is able to help here). http://forums.vega-strike.org