The obvious first and easiest step is to see if the software runs in windowed mode: this involves no changes, hacks, or workarounds, but might result in poor performance. The performance issue may be a non-starter though, because the problem implies OLD software.
The term you are looking for is
aspect scaling and/or
image scaling and the method depends upon the software and the hardware drivers.
There is a way to pick unsupported display resolution for that game ( http://www.widescreengaming.net/wiki/Warcraft_3 ), but it does stretch.
HKEY_CURRENT_USER\Software\Blizzard Entertainment\Warcraft III\Video
reswidth = 1920 resheight = 1200
The driver scaling depends on the hardware and the driver VERSION, but for ATI/AMD catalyst drivers: ( http://techreport.com/forums/viewtopic.php?f=3&t=68072 )
Set your resolution to anything below your usual resolution.
- Right-click your desktop, and go to the Catalyst Control Center. Set it to advanced mode if it's not already.
- At the top left, click the "Graphics" menu, and then "Desktops & Displays".
- For your desired display, click the little black triangle in the bottom part of the screen, on the LITTLE picture, not the BIG one, and click "Configure".
- The scaling options will now be selectable, check the "Enable GPU scaling" box and select "Maintain aspect ratio". Hit Apply.
- Set your old resolution back. Even though the forementioned scaling controls are greyed out and you can actually see "Scale image to full panel size" grey-selected, don't worry.
- Go play your games!
Note that the above steps worked for me in one case, but then at another time, with a different version of the catalyst drivers, this did NOT work.
I don't know about nVidia.