gamepad, I know exactly what you're talking about, and it has caused me headaches too. I'm using driver version 169.21 and I can play WC3 on a widescreen monitor (Soyo 24" and Dell E207WFP like yours). Have used 8800GT and 8800GTS G92. I'll try to describe how to set it.
In NVIDIA Control Panel, click on "Change flat panel scaling" under the "Display" section. Select "Use NVIDIA scaling with fixed-aspect ratio." Voila - that should fix it. If it doesn't...
In NVIDIA Control Panel, click on "Manage custom resolutions" under the "Display" section. If "Treat as HDTV" is unchecked, try checkmarking it. If it is already checkmarked, try unchecking it. THEN, try to change the scaling to what I mentioned above.
I've also found out that it dosen't work with certain monitors (but should with your Dell). For instance I had a 22" (or 21.6") Hanns-G monitor that I could not get fixed aspect ratio working, but the same system works fine with two different Dell monitors (E207WFP and E2005WFP).
The other thing is that Nvidia seems to occasionally "break" this, because seems like certain driver versions didn't work with this setting even if the setting was there.
At least Nvidia had it as an option, working or not. ATI just barely got it into their latest drivers.