What processor do you have?
It sounds like you downloaded the 64-bit ISO files instead of the 32-bit ones. The "x86_64" simply means they're built for the Core 2 Duo and Athlon X2 processors. If you have a standard 32-bit processor, then you'll want the i586 ISOs instead. i586 covers everything from Pentium I all the way to the Athlon XP. You'll occasionally see things for "i686" builds, but that's for Pentium II and higher; it's easier to stick with the i586 trees (for safety anyhow). Hope this helps...