Landy, much as I'm with you on logic 'n reason suggesting that it's better to turn it off, apparently it IS better to have it on: Care of a pal o' mine who has a minime I got to read up on this and IIRC it transpires that with said mode on the machine detects the nature of what's interfering (say, the cyclical pattern that a microwave makes) and adapts its pattern to it. The net result is even though it may be dialing bak on the raw speed, it ends up with better throughput by not having to retransmit packets.
I've tried digging up what wi-fi card yon Mac has and for the life of me ALL I can find is "AirPort Extreme" and nary a word on what the actual device is - like the 2200BG in the Dell

..makes it a biatch trying to compare devices. So now, at the very least kilps, is there any chance you can boot up that Ubuntu CD on your MacBook, get into the version of device manager it has and find out whatthehell card IS doing wi-fi duty?
Another question/thought: seeing as Apple has largely come to their senses over the last few years and use commodity hardware, with Intel chipsets figuring highly in that mix, maybe they're using a regular miniPCI card ..say an Intel one (though, from what little I've been able to find I'm suspecting a Broadcom part), or at least something that can be swapped out for something good from the PC-world parts bin ..nigh on anything with an Atheros chipset would do it: the Senao
SL3054MP for B/G or
NMP8602 (senao.com) for A/G come to mind (both, until recently on the Miro pricelist). But of course there's always that pesky 'warranty void if opened' problem to deal with...
edit: *gak* ..my bloody brain saw 'speed' for 'range' on the whole interferene robustness thing; makes me look kinda silly to have been going on about all that!
