I have the same problem with my passenger seat. My understanding is you have to replace the whole seat if you go through the dealer, as they don't sell the motor seperate. I've not been able to locate just the motor, so I'd appreciate any help as well.
Regarding the no heat issue. I'd assume you would need to run a typical diagnosis on the car for this issue. You have a temperature guage, does it take a long time for the car to heat up? Then this is likely your thermostat. Could also be your heater/coolant valve ("****" if the forum doesn't edit the actual term for the part). I know on the older Maxima's, this valve was vacuum operated, so you might want to check your vacuum hoses.
FYI: You can download free FSM's offline. I found you that is password protected...you have to type it in each time to open it.....still free so can't complain too much. I think it was www.pdftown.com
as the address. The passwords are pdftown.com.