Don't get me wrong I love my nice big widescreen display. But with dual monistor this game gets... "interesting" in full screen mode. How can I change it to a windowed mode? The tried and true method of Alt-Enter isn't working. Though maybe I'm doing that wrong.

Help?!

"Run in a window instead of full-screen", does the trick, indeed.
You might need admin rights to save changes using \Primordia\winsetup.exe.

Further setup options:
I liked graphics better with less smoothing filters (like anti-aliasing), but that's a matter of taste.
"Smooth scaled sprites" turned on looks good, though.

For extra reference just in case: the settings that can be adjusted through "winsetup.exe" are stored in a file located in the same game folder, called "acsetup.cfg". That file can be edited manually if needed. The fullscreen/windowed modes are toggled by setting the parameter windowed to 0 or 1, respectively. (Enabling "Smooth scaled sprites" adds antialias=1.)