Games playing @ 800x600!?

['da_n00b]

I recently attached a dell 17" monitor to my HP pavilion dv9000 notebook. Upon starting up a game, I discovered it appeared to be playing at a very low resolution where the screen seemed to be quarter size, and centered in the middle of the laptop's screen. I tried adjusting the resolution in-game to no avail. I also tried various other games, some of which used directX-8 and some directX-9. Still small screen. I have tried unplugging the monitor and playing the game, plugging it back in, using another dell CRT monitor, rebooting the computer, and changing the resolution settings in game. Nothing! I then adjusted the screens actual display resolution in the display settings window for 800x600. Instead of being very large and grainy, the screen was quarter size, just like in the games. Switching back to 1680x1050 returned to full screen (Though games remain small).

This is what I have determined:
1. This is not a problem with the games, but with the computer
2. The game's settings have no effect on it's size on the screen
3. The games appear to be set to play at an 800x600 resolution by default. (probably vista's doing)

How can I fix this problem so that games once again run full screen?

All games are run as admin in Windows Vista Home Premium

System specs are:
HP Pavilion dv9000
Windows Vista Home Premium 32bit
AMD Turion64 @1.8GHz dual-core
2Gb RAM DDR2
NVIDIA Ge-Force Go 7600
100GB HDD
17" widescreen @1680x1050 (laptop)
17" LCD @ 1280x1024 (other monitor)