I have also had power window problems with my Altima. I started having problems with one of the driver's side window. I notified the dealer before the warranty ran out. Since the 36K mile warranty ran out, I have had problems with the passeger and one of the rear windows. I do not know what the problem is. I am debating extending the warranty because of this problem. I am now realizing that more people are having this issue.

There is a recall/service campaign on the Xterra, Frontier, and some Altimas for the window regulators. Check into that, you might get a free fix or warranty extension on them.