I have broadband on my desk top computer.
I have two laptops that access this connection via wifi
how do I secure all three computers so that only computers on my home network can access the wireless and broadband connection.

Are outsiders really able to access the broadband connection or is it just the wireless connection at risk?

Almost universally, home wireless router design places the wireless inside the firewall. That is, anyone who gains access to your wireless has your whole network. They can upload or download anything over your connection, sniff packets and exploit any vulnerabilities.

Use WPA to secure the wireless. It provides a mechanism to control access to the wireless (802.1x) and encryption to prevent snooping.

2Gnu

Since my system is already up and running how to I implement this WPA thing. This is new to me.

Do I have to delete/disconnect my broadband/modem/router? Can I just insert some software?? disk/delete old software and reconfig.

Clueless

you need to access your wireless routers administration features, and the setting should be in there, if it supports it. if it is an older router, it may only support wep, which is still better security then nothing at all.

most today have wpa, though. so if you find the setting it is fairly easy to set.

This step MUST BE DONE on the desktop PC using a wired ethernet cable. just click to WPA-PSK and it will ask you for a passphrase. after you type it in and save it, you must also change the wireless configurations on your laptops, change their settings to use WPA, and enter the same exact passphrase you entered for the router.

In addition to the above at the router end, you need s/w (a supplicant) on the client end to handle the authentication. http://hostap.epitest.fi/wpa_supplicant/