Read the manuals. Wireless networks tend to work without too much trouble straight out of the box. Most people find it best to start simply and check each stage.
Firewalls are often the cause of set-up problems; because they are designed to stop intrusion, they stop intrusion by other pcs on the network. It is often best to disable them long enough to establish the connection, then switch them back on; if it doesn't work then, you can be reasonably sure that it is the firewall.
Similarly with encryption - if it works without, but doesn't with, then it is probably something in the encryption set-up causing the problem.
Norton Internet Security is well rated. If you look in pc magazine reviews it is usually amongst the leaders. It would be best to have it installed on all the pcs rather than just one, since then it will help prevent nasties getting in; if they do get in, it will stop them getting out again.
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