Can I upgrade from CS3 for Windows to CS 6.5 for Mac? If so, How?
The current version of CS is 6 not 6.5 At the end of December you will loose the ability to upgrade to version 6. You need to call Customer Service to do a cross grade from CS 3 Windows to CS 6 for Mac.
What Michael said.
You have until 31 Dec 2012 to upgrade from CS3 to CS6 (or in your case "crossgrade").