It is very easy to do and I set the same thing up for my parents in less then an hour (well, the basic setup up anyway!)
You can replace the existing modem with an all in 1 but why bother? I have a wireless router plugged into the bb modem via an Ethernet cable. The router I have is a Netgear WGR614. In my PC I have a Netgear WG311. Plug them in and they work (of course now you need to enable encryption MAC filtering etc...)
I would recommend you get a router and network card from the same manufacturer.