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Doesn't work how?
Does your network show up in the list of available networks under Airport?
What does it say under Sys Prefs > Network > Status: Airport? Is airport enabled?
Are there security settings set on the router that might make it difficult for airport to find it automatically (eg MAC filtering, SSID broadcast off)?

If the SSID (the network's name) is not being broadcast it won't show up in the list of available networks under the airport icon in your menu bar (presuming it's showing up there?) and you have to choose "Other" from the drop-down menu and enter the network name (and any security settings like WPA and password) manually.
 
[EDIT] this post was accidently edited by me. Below is only part of what I posted. I was trying to recycle text and got confused as to what thread I was in.

Get a program like Kismac or iStumbler or MacStumbler so that you can get better metrics on your signal strength. iStumbler now has a Widget that connects to the program if your running it. Kismac is my preferred wireless tool. A nearly static graph with 5 levels of information (as seen in the menubar) isn't as good as one that has the potential for hundreds of lines of resolution over time. You can find the "sweet" spots as well as dead spots in your house with these tools. You can find other networks that might be interfering. It might help you position your network hardware better. It's also nice to have a good stumbler for when your out and about.
 
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