People have reportedly been able to upgrade to newer AMD cards, such as the 7970, but they aren't officially supported. If you can find a newer one with the standard MXM slot - of the beauty of open standards!!! 🙂
- then you should be able to put it in, install (update) the drivers, and things should work. Sorry I'm too familiar with this situation, as I don't have the G73JH, and I am going on hearsay from the forums (and internet at large).