I strongly recommend that you Check-in to Your Profile > Select product (Weapon for FSX) > Extended Download Service > Get New Links and download another installer and try that. If you still get the NOT COMPATIBLE message, something is conflicting with it. I am using it in Windows 7 64bit and it works perfectly fine.

You could try installing it with your Anti Virus software disabled or turned OFF (turned off would be the best) as it might see the Weapon for FSX - Loader as a virus or malware. My Anti Virus program is Avast Free v6.0.1203 and it doesn't see the Weapon for FSX - Loader as a virus or malware on my system. Not sure of other AV Software though.

It could also be worth downloading the new installer with the AV Software OFF.

Mark