If you have an Athlon, the installer should properly detect that and
install the athlon kernel. If it doesn't, that's a bug.
There's also now a (undocumented, could go away someday) boot time
option that you can use with 'linux rpmarch=i586' to override the
detection for all those people that have asked about doing the install
on an i686 machine and then moving the hard drive to their i586 box
afterwards.
Ooh. Since the installer is doing auto-detection of arch, I do hope that
option doesn't go away. I have a NSC Geode here that most things see as
i586, but it doesn't have a working TSC so the pentium kernel will
generally crash, and it actually performs better with i486 code (despite
supporting MMX).
Odd hardware like this is far from unknown, so if nothing else the
option to force the use of i386 packages would be handy to always have.
There's also the install portability issue previously mentioned.
Craig Ringer