Just to correct/add to my above post;... from what I read(correct if wrong), if the 32 bit app is "large address aware", then it should be able to use up to 4gb ram in a 64bit OS. In a 32 bit OS, by default, 32bit apps will only use 2gb max. 

Some programs are rumored to crash if they exceed the 2gb limits as well, so hopefully someone can confirm if Carrara is large address aware for those using more than 2gb and a 64bit OS.