I'd been having some issues with the wireless in my macbook for the last month or so.
It was only picking up really strong/close wireless access points. I first thought it was a software issue as there have been some issues with mac os and wireless of late.
Anyway I tried Windows XP and was getting the same problem.
So after a lot of playing around I opened up the macbook to make sure that the antennas were connected correctly; they were.
So tonight I tried replacing the airport (wireless) card with another one. The original macbook uses an Atheros 5006X wireless chipset (Mini PCI-E). I used a standard PC Atheros AR5006EG (ar5bxb61 (em100)) card and it worked straight away. The mac thinks it is the same card that was in it before, except that the mac address has changed and that the wireless now works!
So it looks like the airport card was dead, sort of. But I'm happy now my wireless works.
This macbook hasn't been all that reliable. I've had a dead hard drive, replaced the top casing twice, had my battery die and had the wireless die. Saying that 1st gen apple products are known for their issues. I will keep using macs for laptops and PCs for desktops.