Hello Mr. Callicott,
If you are base on AutoCAD make sure to install the proper version on your new machine (64-bits) automatically it will install in in the good format. if you are base on the standalone, for the version 2012, it is only available in (32-bits) so again you don't have to worry. I have a good new for you, the 2013 version is in 64-bits and it is available!
Regards,
Olivier Gervais