Can I install P6.1 on Windows 7 Pro 64bit?

You can do so, but it may be slow as there are no tested configurations on installing that version on a 64-bit machine. With that said, because our client application(s) are only 32bit, starting with P6 v7, the client application(s) come equipped with a /LARGEADDRESSAWARE option that allows it to address additional virtual memory above 2GB. Applications that are compiled with the /LARGEADDRESSAWARE option are able to take advantage of the /3GB switch in 32-bit Windows and will automatically be able to address up to 4GB of virtual memory in 64-bit Windows.