Unplug the power cord (you should have done this already), the big mobo power cable (1.0/1.1: just pull it really hard while wiggling, 1.2-1.6: there is a small clip you have to push), and the HDD power cable.
The PSU is held in with two torx 10 screws, they are on the left side, one in the front, one in the back. Remove the screws, then pull the power supply forward, then up.
On the backside where the power plug is is where you need to strengthen the solder joint.
Thanks heaps - looked far more complicated than it was! V1.0 box, built early 2002, with a foxlink.
Half an hour, and my xbox is back in original order. I re-soldered the pads, and added some superglue under the front edge of the plug to make sure it doesn't rock any further. Was definitely a foxlink, and was definitely busted - the solder pads were cracked in the middle.
My replacement cord arrived today - the aussie version has the 'module' in the middle of the cord... A wall plug, 1.5m of cord, then the unit, then another 1.5M of cord... don't need an extension lead now anyway