./configure --disable-distcc --enable-xvmc --enable-dvb --dvb-path=/usr/src/kernels/2.6.15-1.1831_FC4-i686/include/ --enable-opengl-vsync --enable-proc-opt --enable-firewire --enable-dvd --libdir=/usr/lib
This should have enabled firewire, but no dice. Looking in the script, I found that it was using pkg-config to determine the version of three libraries: libraw1394, libiec61883, and libavc1394. The strange thing was that I appeared to have recent versions of all these libraries installed, yet pkg-config didn't think they were recent enough.
A large amount of googling and thinking later, I realized that pkg-config relies upon rpm installers placing ".pc" files into the /usr/lib/pkgconfig/ directory, and I had no ".pc" files for any of the three critical libraries. I downloaded the source trees for each library and discovered that libiec61883.pc, libavc1394.pc, and libraw1394.pc were located in their respective packages. So I copied them into /usr/lib/pkgconfig, and now mythtv configured properly. I was able to make and install a version with Firewire enabled.
We'll see how that turns out.