MSI p6n Diamond (BIOS V1.3) - problem with 8GB (4x2GB) 800MHz CL6 RAM

System specs:
MOBO: p6n diamond (BIOS V1.3)
CPU: Q6600 @ 2.4GHz
PSU: Chieftec 650W (CFT-650A-12B)
OS: Vista SP2

Background:
I bought an 8GB (4x2GB) 800MHz CL6 (6-6-6-18-24 1.8V) RAM kit (amazon.co.uk/Komputerbay-DDR2-DIMM-800Mhz-6400/dp/B...