Download VCStarter 1.70 BETA tool. Rename your old Vietcong.exe to something like Vietcong_old.exe. Extract tool and place all files in the Vietcong folder/directory. Run VCStarter.exe first, click apply, then run vietcong.exe to start the game.
If you want to run the Fist Alpha addon, then right-click on vietcong.exe, select "Send to", select "Desktop (create shortcut". Right click the new shortcut, select "Properties", in the Target field change it to: "C:\Program Files\Vietcong\vietcong.exe" -addon fistalpha and click apply. Double click the shortcut to run Vietcong with the Fist Alpha addon.