Basically the whole RRoD problem is because of some connections inside the console that have come loose. The kit provides a couple of tools and some instructions to solder those connections back on - I don't remember exactly what the kit contains, but I can ask my dad for info and/or a link to whoever sells the kit when he gets home.
you're worth $300, slim
Great news: The repair kit my dad bought worked, and my 360 has been brought back from the grave. Pretty good value for a £10 kit, eh?