Here is something you can try.
Open up display properties by right clicking on the desktop and selecting "Display Properties"
Click the "Settings" tab
Click the "Advanced" button
Click the "Monitor" tab
Uncheck the "Hide modes...." box
Now use the "Screen Resolution" slider to select 1400x900.
Click "OK" and you're done!
I have the exact same issue: same chipset, xp professional, same desired res (1440x900), also tried installing the driver from intel that is supposed to specifically fix this problem.
It doesn't work, and Robert_U's suggestion doesn't work either.
Here is my solution: WORK 100%
Window + X > Open Device Manager > Display Adapter > Intel(R) G33/G31 Express Chipset Family (Microsoft Corporation - WDDM 1.0) > Right click > Disable.
Then you will have a black screen. Don't worry, force stop your computer by press power button in 5 secs. Turn it on, make sure you plug in your 1440x900 monitor. Window 8 and 10 will automatic detect the suggest screen resolution
Nope, this didn't work, the external monitor Dell 1909W remained in 1600x900 mode, and I am trying to get it into 1440x900 mode.
Have you tried uninstalling the graphics drivers from device manager and then let windows install the default drivers?