Despite the instructions in the manual to edit the registry if a cd change wasn't recognized by WXP guest, my system simply wouldn't list the contents of a new cd (or dvd) but kept insisting that the contents of the cd initially installed were still valid. I was able to work around this by issuing an eject command in the guest system. Unfortunately this has to be done every time I load a new cd but it's much better than rebooting the guest.
Hope this may help others who may have the same problem.
Allan