I bought this game before Xmas for my son and experienced the same issue as most on my iMac. After a bit of digging, the following web site provides a solution...

http://forum.hardmac.com/index.php?s=5cb01280f994f9e87c9ce82ba89302a5&showtopic=259&st=0&p=1286&#entry1286

For those of you who are scratching your head at this point, this is what needs to be done ( I'm no OS X guru, but eventually got what I was after from Google.... )

1) Load DVD
2) Install game
3) Run Intel patch
4) Fire up Terminal ( you can find this in the applications folder under "Utilities" )
5) At the Terminal command line type

cd /Volumes

then hit

6) Still in Terminal type

sudo ln -s DISC1 DISC2

then hit

7) Enter you OS X Administrator password and

8) Go back to the icon for Cars and run the game

It appears that you have to repeat steps 4 - 8 every time you need to play ( with DVD insterted ) - if there is anyone out there proficient in OS X
UNIX and knows how to make this aliasing
stick please let me know.

Thanks go to the author of the forum mentioned above - "Cri-Cri" and friends "Grambo" and "MacBidouille"