OK so it was pretty early in the morning when i asked my questions, and hadn't bothered looking into diodes too much at 5am (AUS)
So i have since learnt that diodes do have polarity, and that Australian electronic stores dont stock anything i need, ever, I will shop online from here on in. Jay-car only stocked n4004 (higher amps but i bought them anyway for a shiny dollar.) and didnt have any SP3T switches.
I can only dream of what it must be like walking into a radio shack...
Still not sure exactly how much heat the diodes will create, and i remembered the main question i was meant to ask
Will i need more diodes or different ones if im running 4 of said fans **EDIT** I now realise i may have to buy a Bugatti Veyron as my current car wont cut it.
And if all this is too much then ill Go the mosfet/pot method, and heatsink the crap outta the mosfets, and put a fan on them which soughta defeats the purpose, im still totally in the dark about what MOSFET i need. im pretty sure a 10k pot will surfice. All i know is anything i make myself would have to be a hundred times better than any of the Firestarting pc fan controllers out there, most cant handle over 4watts a channel.
Stevo,
nice job on machining down the heat sink on the gpu, ive never read of anybody else doing it. How old is your xbox? curious if it was heat related warpage. I had the same problem on my xbox, on both cpu and gpu sinks, Id say doing this would of reduced the temps more so than the fan. Have you replaced your thermal grease with a ceramic type? Have you considered replacing those awful X-clips with some washers and screws?(stops the cpu/gpu dies from separating from the board after long use)
I sent some diodes in series to the Australian board of energy and conservation today, Soughta expecting the doctor to rock up at my place anytime soon, con me into his Delorean and make me go back in time to kill the inventor of diodes
Now you've got a new trick up your sleeve for working with low power electronics. 
