i dont think you're board will support the cpu cause the board supports a maximum fsb of 400mhz and the celeron d has a fsb of 533mhz. your board's chipset is the intel 845 which supports p4 processors up to 2.4ghz and celerons up to 2.8. it doesnt support the celeron d.
if you keep with 478, you wont need to get a new heat sink and fan.
Core 2 Duo E6600 2.4GHz
ASUS P5N32-E SLI Motherboard
2X Seagate Barracuda 500GB HDD
2X Corsair XMS2 1GB PC 6400 DDR2 800MHz RAM
MSI NX8800GTS 640MB
2x Philips 22" 202P73