You need the kernel-devel.*.rpm that matches your current rpm installed kernel.
To list what you have.
rpm -qa | grep kernel
Should see something like this based on info above.
kernel-2.6.15-1.2054_FC5smp
kernel-devel-2.6.15-1.2054_FC5smp
Then you should be able to build madwifi
Also you could find and rpm for your kernel version at the
http://www.atrpms.net/
Even though mention in the stanley doc, just getting the file manually instead of using a updater like yum or apt should cause no issues.
To install as root ' rpm -ivh madwifi*.rpm '
Lots of other post here on madwifi under fedora with more detail. Search here and google for more info as well.
Brian1