Ben,
So when you got the configuration right the driver still failed, because the IRQ was already allocated.
the funny thing is: the lirc_serial driver *does* work when share_irq=1 is added to the parameters specified in /etc/modprobe.d/lirc_serial.conf. At least, I can now happily use my remote control to navigate through MythTV.
If you like, I can send you the dmesg ouput of the now working configuration (but not before tomorrow night, I'm afraid).
Regards -- Torsten