get a wireless router for your laptop and pc
(as long as your pc and laptop have wireless on there)
Reading your post you cant have wireless on the laptop so you just plug it into one of the ethernet ports
Routers have hardware firewalls and port blocking. ive not run a firewall since ive had my router and not one problem with people getting in etc
An adsl router make sure you get one with a built in adsl modem it distributes the dsl through the wireless or through the ethernet ports on it, a switch only transfers what is plugged into it, ie 4 machines
the router will also have 4 ethernet ports which you can plug your xbox into, and all will be able to use the net at the same time