My main concern is a the Motherboard and the PSU
For your motherboard, AVOID GIGABYTE!!! They are often plagued by a bad bios with little to no options. Instead, opt for an ASUS, or a DFI.
New P45 ASUS mobo: http://www.hardwarelogic.com/news/132/ARTICLE/4032/2008-07-28.html
http://www.newegg.com/Product/Product.aspx?Item=N82E16813131296
Actually, right now is an odd time for buying a motherboard, as the chipset technology is in transition. But, you can always buuy an INTEL 945 based motherboard or an X38.
Avoid cheap power supplies. Try an 80+ power efficient one like a Thermaltake Toughpower series, an OCZ, Cooler Master, Zalman, Sunbeam, AXP / Xion, Sirtec, Akasa, Corsair, Antec..... (At least 500 watts and ATX 2.0 compliant)
http://www.newegg.com/Product/Product.aspx?Item=N82E16817153034
http://www.newegg.com/Product/Product.aspx?Item=N82E16817139001
Box + PSU from Antec (plus it's silent); The Antec Sonata III:
http://www.newegg.com/Product/Product.aspx?Item=N82E16811129024