Apologies for bringing up an old thread, but I had this problem recently and solved it. As far as I'm concerned there's nothing wrong with HIS keyboard, just all the new aluminum thin keyboards in general. I recently had exactly the same problem, but I assumed that it was the fault of OSX Leopard, because i got them both around the same time.
With the release of OSX Leopard, or possibly the official release of bootcamp, I found an option in system preferences, and in bootcamp to select target disk mode when you restart, which I had to use to start into bootcamp because the option key wasn't working on boot up.
The problem I had was that when using parallels to run my bootcamp partition, it crashed and i had to ctrl-alt-esc it to death. I thought nothing more of it. Then a few days later I booted into boot camp using the target disk mode, and booted into a broken windows partition which was damaged from the crash. I was completely screwed - the mac was continuously trying to start into windows but the partition was dead, and I couldn't use option to select a partition. It wouldn't even recognise the OSX boot CD.
Eventually after calling customer service who had no idea, I just replaced this aluminium keyboard with my old clackety button one that shipped with macs 2 years ago, and it recognised the alt key absolutely fine, booted into OSX, turned on parallels, and the windows partition fixed itself. But it i hadn't had the old keyboard I wouldn't have been stuck in a never ending cycle of booting into a dead partition.
Fix the aluminium keyboard please, whatever's causing it.