My friend has a MBP that was bought 2 or 3 years ago, and I need to help him prepare some software to run. What are the chances he won't be able to boot from a 64bit Linux live USB flash drive?
If it was bought new, it's extremely unlikely that it's not 64-bit. Only the very first "February 2006" MacBook Pro 1,1 and 1,2 revisions had 32-bit Core Duo CPUs - all others have been 64-bit. There's a nice summary of models on Wikipedia.
I'd recommend he check rather than assume based on age. Here are directions on How to tell if your Intel-based Mac has a 32-bit or 64-bit processor