Sid Meier's Alien Crossfire

Go to the gameDir and edit "Alpha Centauri.ini". Insert this line below the [Alpha Centauri] header (*NOT* below the [PREFERENCES] header):
DirectDraw=0

Then, launch the game, and once you are in the game proper, it will use your desktop resolution. Do *not* attempt to play the game in Classic Mode. That will create the same problems that result from not having the expansion pack. If you want to play Classic Mode, you should first change DirectDraw to 1, which forces the game back to its default resolution of 1024x768.
1280x720 is not recommended. Some of the widgets are taller than 720px and will become misaligned and/or have parts of them cropped off, reducing their functionality.

The game has a couple of "fullscreen" items, and there are some minor problems in widescreen. For example, the "Book of Planet" screen becomes windowboxed, and the text is misaligned.

Also, the monument screen is no longer fullscreen, but a borderless 1024x768 window anchored at the bottom of the screen, with the game world visible behind it. All FMVs force your monitor into 640x480 mode, and most of them are letterboxed.