thanks for your posting.

As far as I know, the IR port is hardwired to the iPod dock connector 
(it also works without a Mac connected) and does not send any signals 
over the USB cable connected to the Mac. Without even a physical 
connection, there's no chance to actually receive those signals in 
any way.

You can, however, use Remote Buddy with your PowerBook G4 (and any 
other PPC Mac with a USB port and capable of running OS X 10.4) using 
a "Keyspan RF Remote for Front Row". It also only has a tiny RF USB 
"dongle" (there's probably a better word for that) and thus also is a 
much more fitting choice for a notebook than a dock with cable.

Finally, the RF Remote is also cheaper and has three additional 
buttons that can be very handy :-)

Check out the "Supported remote controls" page here for information, 
images and links to shops in Europe and the US:

http://www.iospirit.com/remotebuddy/supportedremotecontrols/

Best regards, 
Felix