PPC users + C2D = All of the 64-bit
Intel Core Duo + Old PPC = All 32 - bit
Which is more?
First note that G3, G4 and G5 are all referred to as PPC chips. Out of those, only the G5 is 64bit.
Lets look at the introduction dates for G4s and 64bit Apple systems. I'm going to assume Apple will not be supporting G3 systems, although we don't really know that officially yet.
When did things go G4;
G4 Powerbook - Jan 2001.
G4 iBook - Oct 2003.
iMac G4 - Jan 2002.
PowerMac G4 - Oct 1999.
Mac mini G4 - Jan 2005, replace with Intel 32bit Jan 2005.
There is also the Cube and the eMac.
When did things go 64bit;
Macbook Pro - Oct 2006.
Macbook - Oct 2006.
G5 iMac - Oct 2005, downgraded to 32bit Intel Jan 2006, upgraded to 64bit Intel Sep 2006.
G5 Powermac - Aug 2003. Replaced with the Mac Pro (64bit) Aug 2006.
In the "second quarter ended March 31, 2007 Apple shipped 1,517,000 Macintosh® computersr, representing 36 percent growth in Macs over the year-ago quarter". That means for the same period a year earlier they only sold about 1.1 million Macs. The numbers are going up, but not enough to have eclipsed the 32bit systems, yet.