Core 2 Duo descendants (T5xxx / T7xxx / T8xxx / p8xxx) are 64bit CPUs, Core Duo descendants (T1xxx / T2xxx) are 32bit CPUs, its best to check @ Wikipedia first:
http://en.wikipedia.org/wiki/List_of...icroprocessors
http://en.wikipedia.org/wiki/List_of...icroprocessors
Recently they also added T3200 (Code Duo) and T5800 (Code 2 Duo) CPUs which are not listed @ Wikipedia.
You can also check Intel's Processor Finder:
http://processorfinder.intel.com/det...px?sSpec=SLAVG
http://processorfinder.intel.com/
Imho get used Dell Latitude / IBM/Lenovo ThinkPad with Core 2 Duo t7xxx / t8xxx.