Advice on Windows 7 64 bit upgrade

MC 4 should work, but you'll have to set it to run in 32-bit emulation mode since no version of MC is 64-bit compatible.
The M-Audio may need 64-bit drivers to work, or set it to run at 32-bit, too.
Your projects should load up just like on your present machine.
If loading MC 4 on the new computer doesn't give you 4-track recording, use the old computer. You can have MC on different computers as long as only 1 is used at a time.
Another note; MC Pro 24 is the only version that officially allowed 4-input recording. All other versions are 2 input only.

Maybe a misterm.
You can record one input on multiple tracks; you can't (with most MC versions) record more than 2 simultaneous inputs.
You can record 1 stereo track or 2 mono tracks simultaneously, but no more than those 2 inputs.

Mute all tracks, and listen to each separately, make sure you are not recording the same thing on two tracks.