XP mode. When my work PC was upgraded from Win XP 32-bit to Win 7 64-bit, I couldn't open my Acronis backups. The new, 64-bit Win7 version of Acronis couldn't handle the files.
So I installed XP mode, installed Acronis in the XP virtual machine, and recovered my files. Let me know if you are interested in this approach. Make backup copies of the important files first, JUST IN CASE.
I would also suggest that you contact the makers of Autocad and upgrade to a Win7-compatible version, after they promise in writing that it will open your older files.