Vista Will Not Permanently Keep Native Resolution

I have a HP Pavilion a6110n PC, with a HP w173 Wide LCD monitor. The monitor
has a resolution of 1440 x 900. The video adapter is a NVIDIA GeForce 6150SE
nForce 430. I have updated the driver to NVIDIA 7.15.11.6925 dated
12/11/2007. I have also updated the monitor driver to HP 1.0.0.0 dated
2/6/2007. The adapter and monitor drivers were updated after I read that on
the Microsoft web site that Windows Vista has a problem displaying a systems,
etc. "native resolution". Therefore, I upgraded the drivers. The problem
began after I upgraded to Vista SP 1.

The problem is this. The "native resolution" of 1440 x 900 will not stay in
place. After a few days, for some reason the display reverts to a lower
resolution. The only way I can get the 1440 x 900 resolution back, is to
uninstall my updated drivers, and then reinstall them again. The corrects
the problem, until for whatever reason it reverts back to a lower resolution.

What can I do to correct the problem?
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Thank you.........Pedum