Airtunes/Airplay not working in iTunes 9.2.1 via Airport Express (2012 model)

I bought an Airport Express device the other day specifically to stream music from my Macs to my stereo.

After installing the device I played a bit of music on a Mac running Lion. No problem at all.

However, I own an old Powerbook G4 1.5 GHz as well. This laptop runs 10.4.11 because Leopard is just too much to handle for this old laptop.

So, I tried to test the Airport Express. I can see the speakers in iTunes 9.2.1 but when I try to click the speakers iTunes "hesitates" just a little bit and reverts to "Computer".

Has anyone ever encountered this problem?

Is there a fix? (Besides making my laptop unusable by upgrading to Leopard?)