Is my wireless network secure?

Hi There:
I am using a Speedstream 6520 router, which was provided by the ISP, and I am also using Linksys Speed booster wireless G adapters for my other computers at home. The question is: my friends bring in their laptops and they can log on to my network as soon as they pick my network's name! Is my network secure? If not, do I have to start from scrap all over again to set up a secure network? Thanks.

It sounds like it's wide open.

You need to log into whatever is acting as the wireless access point (sounds like it's the router in your case) and turn on WPA encryption with a long passphrase (at least a few words, or just a long bunch of gibberish if you keep a copy written down). It's important to do that step over a wired connection, because all your wireless connected clients will drop off the network when you do.

Then go to the wireless clients and disconnect and reconnect the wireless network. When you reconnect, you'll be prompted for that passphrase you set.

That's all you need to do.

Page 21 of the manual here gives the details of how.