Assuming your using a DSL based BB connection and not cable you'd be best off getting a ADSL modem router combined.
You'll then use the router/modem combo instead of your current modem. The phone line plugs into the back of the router in the correct place and then it connects to your PC via a network cable and the laptop can connect wirelessly.
I have a netgear model which came with everything I needed in the box and was very easy to set up. Just a case of entering my logon details via the router setup page and enabling the security features once all was running.
Things to look out for are does it have a hardware firewall? What wireless encryption methods does it use WPA encryption is better than WEP. If you want to share large files over the network then you may want to go for a model that has a faster transfer rate. If you do go for a model that employs higher speeds thou you will need to use the manufacturers wireless card/usb device and not the built in wireless card in the centrino laptop.
Hope that helps.