Building a new gamers form factor PC

Im going to America on August 1st and would like to take the opportunity to build a cheap new portable desktop PC. Ive never built a desktop PC before and im looking to build a portable desktop; one that can fit in my carry-on bag as i often travel between countries. I was looking at the XQ pack as the case and would like some recommendations on how to achieve the best portable desktop pc. I have a budget of around 1800 - 2000 $ and will use this pc for gaming / 3d modelling. Also has anyone brought a media centre PC in their carry on through airport security before? Is it allowed and do you think ill have any hastle besides the usual explosive swabs.

This is my build so far:

Case : The most important part. Im not sure at all how to go. I found this one on newegg that looked quite good:
Thermaltake LANBOX Lite VF6000BNS Black SECC Gaming Cube Computer Case - Retail
http://www.newegg.com/Product/Prod [...] 6811133045
80 $ after rebate and shipping

Power Supply :
CORSAIR CMPSU-750TX 750W ATX12V / EPS12V Power Supply 100 - 240 V UL, CE, CB, TUV, FCC, CCC - Retail
http://www.newegg.com/Product/Prod [...] 6817139006
110 $

Motherboard : I really have no idea about the motherboard. Any micro atx with crossfire? will this fit in the case?
BIOSTAR TForce TP45HP LGA 775 Intel P45 ATX Intel Motherboard - Retail
http://www.newegg.com/Product/Prod [...] 6813138123
130 $

CPU : Not sure whether to get quad 9450 or new phenom black edition CPU. What do you think?
Intel Core 2 Quad Q9450 Yorkfield 2.66GHz 12MB L2 Cache LGA 775 95W Quad-Core Processor - Retail
http://www.newegg.com/Product/Prod [...] 6819115042
350 $

CPU Cooler :
ZALMAN 9500A 92mm 2 Ball CPU Cooler - Retail
http://www.newegg.com/Product/Prod [...] 6835118223
$53.99

Graphics Card :
2x POWERCOLOR AX4870 512MD5-H Radeon HD 4870 512MB 256-bit GDDR5 PCI Express 2.0 x16 HDCP Ready CrossFire Supported Video
2x http://www.newegg.com/Product/Prod [...] 6814131113
600 $

RAM :
OCZ Reaper HPC Edition 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit Desktop Memory - Retail
http://www.newegg.com/Product/Prod [...] 6820227267
65 $

Hard Disk :
Western Digital Caviar GP WD10EACS 1TB 5400 to 7200 RPM SATA 3.0Gb/s Hard Drive - OEM
http://www.newegg.com/Product/Prod [...] 6822136151
200 $

DVD drive :
LG 20X DVD±R Super Multi DVD Burner Black ATAPI / E-IDE Model GSA-H55NK - OEM
http://www.newegg.com/Product/Prod [...] 6827136117
$22.99

Thermal compound:
Arctic Silver 5 Thermal Compound - OEM
$5.99

Total Cost: 1600 $


Im open to any suggestions and also wonder if there is anything i need to know when building. IE. do i need to buy thermal paste or does it come with CPU and also how to apply it?
Not certain about motherboard or if i can crossfire in a small case even. Help appreciated!

Thanks for all the help everyone

P35 built in Wifi: http://www.newegg.com/Product/Prod [...] 6813131196

X38 (Crossfire board) with Wifi: http://www.newegg.com/Product/Prod [...] 6813131218

That Biostar board nor any of these boards I picked will fit that case. mATX really limits your options and excludes multi GPU solutions in all cases. You might want to rethink this choice.

Help