The MacPorts Cdrtools package is handy, but seems unable to find the CD player by default: you get something like "No matching device IOCompactDiscServices"
The thing is, with Mac OS X 1.5.x, the service is different, and it's called IODVDServices.
So in order to rip a CD, you need to issue the following command:
$ cdda2wav dev=IODVDServices
The it should complain about being "Unable to get exclusive access to device"
In that case, you should umount the device (find out which one it is with the "mount" command), and then everything should work fine (You might need to quit iTunes if it's launched though)
$ mount
...
/dev/disk1 on /Volumes/Audio CD (cddafs, local, nodev, nosuid, read-only, noowners)
$ sudo umount /dev/disk1
$ sudo cdda2wav -t1+27 dev=IODVDServices