Just downloaded this new mod for Half-life earlier. I wanted to play on the net, alas, steam didn't find any Australian servers. :(
So I raced around a little by myself, and I have to say it's a good effort. The physics seem to fairly good, but not perfect. Think of it as V rally for Half-life. except not as good.
But there are a few nifty features in the game, too. You can buy different tyres, etc from money you earn.
Download it here:
Half-life rally