airport express with USB modems

I'm also interested in this, the USB port on the AE can surely make use of a modem as well as a printer?

No, the usb port cannot be used according to AirPort Extreme, AirPort Express: Uses for the USB port.
For a friend of mine (in the UK), I replaced the ADSL USB modem with ADSL X-Modem, which works nicely, but isn't used in a wireless network there. According the reference the X-Modem works with Airport Extreme, I haven't seen a reference about Airport Express (maybe someone else has experience or a reference), but I can imagine it does work, too.
HTH

] I have an ibook g4. will an airport express station work with my USB modem to give me wireless internet?

No you can not use a USB modem with the Airport Express, as the USB modem requires a computer to work correctly and the USB port on the Airport Express is for limited purposes only.

AirPort Extreme, AirPort Express: Uses for the USB port
http://docs.info.apple.com/article.html?artnum=107857
http://docs.info.apple.com/article.html?artnum=300872

You will need to get an ethernet ADSL modem which supports PPPoA.
] oh, and does anyone know whether wanadoo broadband will be compatable?

With an ethernet ADSL modem, an Airport Express your iBook will be able to connect to the internet using Wanadoo, however you may not get the support from Wanadoo.

http://www.adslguide.org.uk

] According the reference the X-Modem works with Airport Extreme, I haven't seen a reference about Airport Express (maybe someone else has experience or a reference), but I can imagine it does work, too.

It will and it does.

] I'm also interested in this, the USB port on the AE can surely make use of a modem as well as a printer?

It won't as the USB modem requires a computer to function and the Airport Express is acting as a print server.