Usually when you go to System, Hardware Drivers it gives you a choice of
graphics drivers. Is that the case? If so, have you tried using a different
one? It seems to me that you have the wrong graphics driver installed for
your card. Even the open source Nouveau driver will give you better
resolution.

Some conversations re: your problem (just google your problem for more)
www.linuxquestions.org/.../%5Bubuntu%5Ddriver-not\
-working-for-nvidia-6150-se-geforce-717941/
forums.linuxmint.com/viewtopic.php?f=59&t=8430
alan.lamielle.net/.../installing-nvidia-driver-185-18-14-with-real\
-time-linux-kernel-2-6-28-3-rt

Have you considered running Ubuntu 10.04? It has a newer kernel and better
graphics drivers and has three years of support from Canonical. Also you can
run Quicken in a Windows client VM inside Ubuntu host using your new dual
core Athlon provided that you have enough RAM to make it work efficiently.