I have windows 7 installed on my pc.i installed
Well, try this, we call this "compatibility" mode, most programs can be run on windows 7 with this trick.
I assume your Cossacks II Napoleonic Wars icon is on the Desktop,
Right-click the Icon (game's icon), select "Properties" and click "Compatibility" tab, select "Run this program in compatibility mode for" click the "Windows 95..." and select "Windows Xp (Service pack 2)", click "Apply" > "Ok" and try again.
If even after doing this, the game can't be played, then there's no option. The fact is that, this game is made to run on system with Windows xp and earlier version, but somehow if fortunate, it's possible, not will all software, some may work, some may not.
Good luck.
Thanks for using FixYa.