STALKER Clear Sky
Install as a mod. While in a game, hit ESC and then F1. You'll see a menu with three columns. The 1-st one is for weapons, 2-nd is for dogs, and the 3-rd - for cars. If you don't want the cars to be so fragile, edit the immunities sections
This mod spawns cars, dogs and weapons by an auxilliary menu. It is an alternative to Helios mod with cars, that I've found on a russian site.