Hi Adam - just wanted to let you know that I agree with your
suggestions. I had the same problem as Ian Wu, with Infrared Monitor
not starting. In the end, I found that irda.sys was missing from my
system32/Drivers directory. I think that Service Pack 2 re/moved this
file, but I can't be sure.
Anyway, I got irda.sys out of the C:\windows\driver
cache\i386\Driver.cab file (using Winzip to do the extraction), and
stuck it in the location you gave. After a reboot, the infrared
monitor service restarted automatically and finally worked.
Took me 4 hours to figure this out - sure wish I'd read your post