That was it! Thanks.
The game runs fine now (practice mode only, of course), with two exceptions: The map scroll speed is very fast, even on the lowest settings, and the menu windows are transparent for some reason (i.e. there is no background and you can see the map or other menus underneath).
Try and set maxfps to 300 in ddraw.ini and HardwareFills to 0 in conquer.ini.