🚀 go-pugleaf

I recently configured an Airport Express unit as a client on our home 
Airport system (complete setup summarized below).  

The instant we began playing music from one of our laptops to our living 
room stereo system through this AE client, doing so seemed to soak up 
essentially all the bandwidth capacity of our Airport base station -- 
connections from a second laptop thru the Airport LAN to the Internet 
slowed to a crawl.  

Is this normal?  Or do we need to upgrade part of our setup?

Full setup:

AT&T DSL comes into house through a Cayman 3220-H modem/router unit (DSL 
installation is very low data rate, maybe 130 KB, due to 25,000 foot 
distance to local office; Cayman router is ancient, was part of original 
installation 7 or 8 years ago)

One of the Cayman's 4 ports goes to Airport Extreme base station that's 
a year or so old via 100' of Cat 4 cable; second port goes to an 
Ethernetted printer; third and fourth ports not connected.

Airport Express unit is new; I configured it as a client on the Airport 
Extreme network following instructions in user's guide.  Nothing except 
an audio cable to the stereo system is connected to it.

Music source is iTunes on a MacBook Pro running OS 10.5; second laptop 
is MacBook running OS 10.4.  Both laptops see the Airport Express as a 
remote speaker choice in iTunes speaker selection menu.

Observed behavior is that Internet response time for second laptop 
attempting to read email with Eudora or surf with Safari drops to a 
crawl as soon as first laptop starting sending music through the AE unit.