Hi Toby,
  Sorry for the late reply. I had a a look at the modifications you made and i fixed few issues. All the modifications i did are in this fine only : http://www.tarektaha.com/mricp_driver.cpp just overwrite it and it should work.
  I also have this driver that i would like to share with you guys http://www.tarektaha.com/wiki/index.php?title=SSPP which is for path planning in tight environments and you can interface with it just like the AMCL, have a look at it.

Sorry for the delays, I have added this driver to CVS, I had to make some modifications to make it build with recent changes to player (and in the player source tree). Thanks for sharing your work, are you able to check out the latest player and check whether it is functioning correctly, i was only able to perform simple tests and it seems that some things may have been broken with the updates and/or with recent player changes.