Apple Gyan: How to tell if your Intel-based Mac has a 32-bit or 64-bit processor

# Choose About This Mac from the Apple () menu in the upper-left menu bar, then click More Info.
# Open the Hardware section.
# Locate the Processor Name.

4. Compare your Processor Name to information below to determine whether your Mac has a 32-bit or 64-bit processor.

Processor Name 32- or 64-bit
Intel Core Solo 32 bit
Intel Core Duo 32 bit
Intel Core 2 Duo 64 bit
Intel Quad-Core Xeon 64 bit
Dual-Core Intel Xeon 64 bit
Quad-Core Intel Xeon 64 bit


for much beautiful page :
http://support.apple.com/kb/ht3696