If you have Linux installed in your computer you can enter the command:
this will list the CPU information for your computer. Look for the line which begins with "model name" for the processor in you system. You can look up (Google) the processor name to determine if it is 32 or 64 bit.
Mine reports for instance in the 5th line:
model name : AMD Athlon(tm) 64 X2 Dual Core Processor 5200+