How do I get an Nvidia 7800GT 256MB video card to display 1440x900 resolution?

It may be, but Windows will only display resolutions of which your monitor is capable. So your problem is probably there.

I agree with Ryan D, you may need a better Monitor. Most flat panel screen are really only good for 800x600. But if you are using a CRT try lowering your refresh rate to 60Hz and then setting your size to a higher resolution

Get an NVidia card. i take advantage of to purchase in difficulty-free words ATI playing cards, yet when I bumped right into a similar subject I picked up the most inexpensive card i might want to locate (an NVidia 6600 PCI-E for roughly 50 money) and it truly works way, way extra constructive then my ATI x700 card ever did. It also outputs a miles extra constructive photo to my HDTV. i don't think of i'm ever paying for a ATI card back.

go to Display properties>>>>>settings>>>>>advanced>>>>>>and choose monitor settings>>>>>>>>try giving a higher refresh rate

Yes, it's limited to your monitor. My Magnavox, for example, can only support up to 1024x768. Not the highest resolution, but it's good for what i need it to do.

have you installed the drivers? then go to your control panel and put it on that resolution...