[dnanian]

Well, what I'd do is install the 750GB drive into the MacPro. Use Disk Utility to properly partition it as "GUID", with one (or more) Mac OS Extended (Journaled) partitions. Then, use SD! to copy -- using "Backup - all files" and "Smart Update" -- from the 250 to the 750.

When the copy is done, rename the destination drive to the same name as the old drive (e.g. Macintosh HD). Open the Startup Disk Preference pane and select it as the startup volume, but don't click restart.

Shut down your Mac, remove the old drive, and start it up again: that should do it.