The Mac version is 32 or 64 bit. OS 10.5, 10.6 and 10.7 are 64 bit and can run 32 bit applications, they were developed for 64 bit Intel CPU's DS4 was the first 64 bit Mac Studio version

64 bit OS's can run 32 bit software with the limitations of 32 bit software, if you have 16GB RAM and run Daz Studio 4 32 bit in Windows 7 64 bit you are restricted to no more than 4GB RAM for the 32 bit application, which is better than the 2GB (by defualt) or 3GB (if you modify boot.ini or cmd line) of all 32 bit XP, Vista, Win7, etc.

So you can install both 32 and 64 bit version of Studio 3 & Studio 4 and use them all four of them at the same time if you want.