So that's where they're keeping it

I've since found a great deal more about multipath in Linux:

• http://people.redhat.com/nayfield/storage/RHEL4Storage.html
• http://geekyschmidt.com/2008/09/15/multipath-and-redhat-linux-5/
• http://www.tuxyturvy.com/blog/index.php?/archives/42-RHEL4-dm-multipath-on-root-HOWTO.html
• https://www.redhat.com/archives/nahant-list/2006-November/msg00044.html

The trick was to search for "multipath" and "fstab".

Also, I contacted the installer from Sun who worked on our new machines, and he told me that the multipath driver download was lost during an upgrade of the download page; they're working on it, but in the meantime he's sent me a copy of the driver. Sweet!