2006-8 MacBookPro -MacBook and MacIntel iMac

2007 - 2008 MacBookPro
MBP 2.2GHz or faster has 2 slots and can support 4 GB Module - to a maximum of 6GB (one 2 and one 4GB module)

2007 - 2008 Intel iMac
24" 2.8 GHz or 3.0 GHZ and 20" 2.0 thru 2.8 GHz can use up to 4 GB
for 17inch 2.0 GHz and 2.16 GHz Maximum is 3 GB.
20 and 24 inch 2.16 GHz and 2.33 GHz Max 3 GB

For 2006 MacBook and MacBookPro
MacBooks and MBPro have 2 slots that can each support 1 GB modules or smaller

2006 MacIntel iMac and MacIntel Mini
Intel iMac and Mini have 2 slots that can each take a 1 GB module or smaller.