ZyXEL 660HW-T1 Mac and WiFi
To midgetuk (04/19/2008):
Your problem is pretty surely Leopard 10.5.2. Sorry that I can't offer any easy solution other than sourcing a copy of Leopard 10.5.1 (or 10.5.0 and downloading the Combo updater for 10.5.1),
When we had a similar problem with our first MBPro in January, Apple Support established, eventually, that the wifi card in the laptop (then running 10.4.11) was faulty. Find 'Network Utility' in the Utilities folder. Open it, click on the 'Info' tab at the top of the screen and then on the Network interface selector. From the drop down options, choose Network Interface (en1) and the box below should tell you that you have an Apple Wireless Interface adaptor with Link Status 'Active' (so long as you have already turned Airport 'on' in the MenuBar top right your screen).
The above indicates that the hardware is working. If not, you *might* (repeat, *might*) have a faulty card (has been a minor issue with MBs and MBPs, I believe), in which case it is a call to Apple Support and its various 'layers' - be prepared for a long wait. If you are within 90 days of purchase (Apple will know from your serial no. on the MacBook) and they can establish it is a hardware fault, a replacement will, quite quickly, be sent. Don't forget to get a case number from the Support line: it is needed to get a replacement on its way.
On the other hand, you will have to wait until the 10.5.3 update, due very soon, which it is hoped will cure these (and other) wireless problems. At least, New York City schools are hoping so, I'm sure!!
http://www.appleinsider.com/ Thursday April 17th
Don't forget that you can still access the ZyXEL box with an Ethernet cable, although I agree that it isn't ideal when you have a portable computer.
This wifi problem is a definite bug, which has appeared elusive, intermittent and very hard to rectify. One consolation is that also seems to affect some people with Apple's own Airport routers. Many others with different third-party equipment, perhaps ZyXEL owners too, have finally got wifi to work with 10.5.2 and wonder what the fuss is about.
It's not much help, but I hope it isn't completely useless. Good luck!