7Z is an archive. Games are packed into those so that you can download them as a single file.
You need to unpack it, and then run the unpacked game in DOSBox.
http://www.abandonia.com/vbullet/showthread.php?t=14406
To start the game, use START.BAT . It will allow you to choose whether you want to play the base game or the expansion and perform additional tasks needed to ensure whichever you chose runs properly.