32 bit or 64 bit?

[Gerhard Magnus <magnus agora rdrop com>]

I'm preparing to download the ISO images for Fedora Core 3 which I will
then burn to CDs.  I'd like to install the OS on a Pentium 4 and on an
older Pentium 3.  I'm assuming I want the x-86-compatible (32-bit)
version for both machines -- is this correct?  What sorts of machines use
the 64-bit version?

Thanks for the help with what is probably a dumb question....
Jerry