"Extreme Gaming" and "a motherboard under £100" hardly go together. Try to see if you can get an ASUS P5B-E or P5B-Deluxe (those two models, specifically). If not, the Gigabyte DS3 is also a good motherboard that should be around your price range. See if you can't find those, and if not, then we'll see if there's others that you might be able to get.
The Scythe Ninja is a find cooler, better than the stock provided one.
PC3200 RAM will not be compatible because, as dario said, you need DDR2 memory for Core 2 Duos. The base memory needed is DDR2-533, but that will not let you overclock at all. DDR2-800 is the normally recommended speed for overclocking a Core 2 Duo.