Shahedz,
You have a wireless ADSL Router which has a DHCP server which is running and suppling addresses to the devices on your network. The Soundbridge being one of them. Is this right?
If so you need to connect to the router via a web browser. Typing in the ip address of the router in the browser address line will bring this up. Find out what IP range the DHCP service is using by looking up DHCP settings. If this is using the whole range 192.168.0.1 -254) then it will need to be changed.
To set a static IP address you must have some spare addresses within the IP address range but outside the DHCP range.
I would imagine the Soundbridge will have a manual setup function. If you can get into the network address settings and change the 'config by' settings from 'DHCP' to 'Manual' You will then be able to assign a static IP address and subnet mask to the Soundbridge. Something like IP 192.168.0.1 Subnet 255.255.255.0 depending on what your ip range is.
I'm working in the dark here but this is the way you would setup a network device like a print server to work on a network. If you want to set a static address on a device you must remove the DHCP settings first.
I don't know if this will help you but for more info you could check out:
http://computer.howstuffworks.com/home-network.htm
Gives a basic overview of how things work.