Building gaming rig - need some help please !!

Hi there, I'm Hamza and I'm new to the forums

I've decided to build a gaming PC, as I've heard it's not too difficult, it's cheaper than buying a preset PC, I can be sure of what parts I install, and above all it sounds fun

I've considered these parts, what I'd like to know is whether these parts will all fit together, whether the case will be a tight fit, and whether there are any better/cheaper alternatives, or whether I could get the products for cheaper at different places. I must specify now that I've ALREADY bought an ATI 4870X2 GFX card as it was going cheap and I couldn't pass off the offer I have about £450 left to spend, however, could stretch to £500

CPU: Intel Q6600 2.4GHZ 'Go Stepping Version' £145 (I reckon I could get this for slightly cheaper somewhere)

[URL]http://www.aria.co.uk/Products/Components/CPUs+%2F+Processors/Intel/Core+2+Duo/Intel+Core+2+Quad+Q6600+2.4GHz+95W+G0+Stepping+(Retail+775)+?productId=28356[URL]

PSU: OCZ 780W ModXStream Modular Power Supply £60

[URL]http://www.aria.co.uk/Products/Components/Power+Supplies/500w+%2B/OCZ+780W+ModXStream+Modular+PSU+?productId=29097&page=2&rqcType=[URL]

RAM: OCZ 4GB PC2-8000 Platinum XTC 1000MHZ £40

[URL]http://www.aria.co.uk/SuperSpecials/Other+products/OCZ+4GB+PC2-8000+Platinum+XTC+(2x2GB)+EPP+(Nvidia+Approved)+?productId=30158[URL]

HDD: Samsung HD502IJ SpinPoint F1 500GB Hard Drive SATAII 7200rpm 16MB Cache - OEM £40

[URL]http://www.aria.co.uk/Products/Components/Hard+Drives/Serial+ATA/500GB+Samsung+Spinpoint+F1+502IJ+SATA2+7200RPM+16MB+cache?productId=33024[URL]

MOBO: ASUS P5Q PEO iP45 Socket 775 Motherboard £100

[URL]http://www.aria.co.uk/SuperSpecials/Other+products/Asus+P5Q+PRO+iP45+Socket+775+Motherboard+?productId=32295[URL]

Case, This is where it gets difficult, I don't know which to choose

1). Antec 900 £70

[URL]http://www.aria.co.uk/Products/Components/Cases/MIDI+Tower/Antec+Nine+Hundred+Ultimate+Gamer+?productId=25541[URL]

2). Thermaltake Armor+ MX VH8000BWS £120

[URL]http://cgi.ebay.co.uk/ThermalTake-Armor-MX-VH8000BWS-Black-New-to-UK_W0QQitemZ310095328598QQcmdZViewItemQQptZUK_Computing_DesktopComponents_RL?hash=item310095328598&_trksid=p3286.c0.m14&_trkparms=66%3A4|65%3A2|39%3A1|240%3A1318[URL]

3). Thermaltake Spedo Advance Case £125

[URLhttp://www.aria.co.uk/Products/Components/Cases/Full+Tower/Thermaltake+Spedo+Advance+Case+?productId=34248[URL]

So what I'd like to know from you guys is, will these parts fit together, and which case do you recommend.

Also, I am interested in overclocking the CPU, would it be worth buying this ?

[URL]http://www.aria.co.uk/Products/Components/Fans%2C+Heatsinks%2C+Coolers/CPU+Coolers/Arctic+Cooling+Freezer+7+PRO+(Socket+LGA775)+?productId=20729[URL]

Thanks for reading and reply soon