Does this wireless contain a ADSL modem, or are you making a connection to the internet via your desktop and ADSL speedtouch modem ? I ask this as I'm a little confused if you've posted the message via the wireless laptop, then you must have a internet connection, and if this is the case and the your only connection is via the speedtouch modem, then obviously the desktop is connected to the wireless router, otherwise the laptop couldn't reach the internet. If this is the case I assume your using Internet Connection Sharing (ICS) on your desktop,
If however the router contains a ADSL modem, then where are you bothering with the speedtouch modem plugged into the desktop ? In this case you'd just setup up your desktop to receive a DHCP address from the router.
Could you clarify your setup ?