Broadcasting Itunes via a wifi router ...

I know my question will seem pretty simple but I am a bit confuse and don't find a proper answer"
I would like if it is possible to send wirelessly my music from itunes with that configuration I have:

G4 quicksilver 933 Mhz
A wifi router Dlink (802.11g) (connected to my Adsl modem) i am it using for wireless access to internet in my home via my Itouch
An Airport express (i would like to buy one if it can work) as a receiver to plug into my stereo to receive itunes remotely and wireless

PLease, can it work? How Itunes will see my wifi router to send thru it?
Or do I have to add a airport card into my G4 (wich can only take old airport card)

Thank you for any help.

Richard

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