Hi Rich,
I am currently running AutoSketch 8 and I have been using this software since Drafix 4. I just tried opening some of my old Cad files from Drafix and when I used the dialog box the extensions listed were Drafix v3 and v4. I just opened a file that was created with v4 with seemingly no problems.
So I would say either version 7 or 8 would do you just fine. I doubt if you will be able to find a copy of version 7 about now.... But mabie some one here can steer you in the right direction. Hope this help! The only real diffence between 7 and 8 is the updates for the O. Systems.
Regards, Tom Mitchell