Balix,
Its relatively straight forward to do. What you need is a Wireless Broadband Router/Firewall. Netgear do a nice flying saucer shaped one that does the job
http://www.netgear.co.uk/html/prod_r...dsl_dg834g.htm it even has a four port Ethernet switch. You will also need a network card for each PC that you want to connect. If the new one comes with an Ethernet port built in, so much the better you plug straight into the 834. A word of warning, if you use wireless you MUST put the WEP encryption on, or you'll broadcast to the world.
Don't worry about FreeServe, they have no way of knowing how many computers are using the ADSL, the beauty of the router.