building a pc?

hey, im need a little help and advice on building my first pc.
i know quite a bit about computers, just not the building side of it. what i need help with is mainly compatibility issues and whether a particular component is just not good enough. also some general advice about the building process would help greatly. here are my components:

Motherboard:
XFX N680i LT socket LGA775 motherboard (misco.co.uk) OR
ECS 650iSLIT-A nForce 650 LGA Socket 775 Motherboard (aria.co.uk)

CPU:
Intel Core 2 Quad Pro Q6600 Energy Efficient SLACR 95W Edition 2.40GHz (1066FSB) - Retail (teckheads.co.uk)

Graphics card:
XFX 512Mb nVidia GeForce 8800 GT PCI-Express VGA Card (eclipsecomputers.co.uk)

Memory:
OCZ 4GB Kit (2x2048) NVIDIA SLI - Ready Edition DDR2 PC2 6400 800MHz Dual Channel EPP 5-4-4-15 Nvidia XTC Heatspreader (eclipsecomputers.co.uk)

Hard Drive(s):
Western Digital Caviar 500GB S300 16mb 7200rpm (dabs.com) (X2)

DVDRW Drive:
LiteON LH-20A1S-10C 20x DVDRWRAM SATA Beige (aria.co.uk) (X2)

PSU:
No idea how much is enough to power this system??

Case:
Thermaltake Soprano SECC Black, Window VB1000BWS (dabs.com)


also what kind of cables will i need. will i need to buy any coolers for the cpu or case? and am i missing anything essential?

thanks in advance!