HI! this is a Power Supply Unit question, just bear with me...
Ive got a PC with a sigma gaming case , a quad core QX6850 (3GHZ), asus P5N-E nforce 650i sli mother board, 3gig of ocz memory (pc6400 ddr2/800), an 8800gtx 768mb graphics card and a hiper type-m sli/crossfire ready 580w power supply, running windows xp home (SP 3),
and every now and then the **** thing locks up on me! (i can move the mouse pointer but clicking on anything doesn't do anything) and i have to ctrl alt del to unlock it, also today for the first time a nvidia box popped up on screen telling me my graphics card wasn't recieving enough power and had adjusted its settings to compensate (or something like that), so my Power Supply Unit's not man enough then? i don't understand all this volts amps etc and am worried that continued use as is will fubar my pc. would this one be ok? will it fit in my pc etc?

Arctic Power 700W Power Supply Unit - With PCI-E, 1x SATA, 20+4, ATX12V, 8pin +12V Connectors - Retail Boxed - Ebuyer

Here is a really good tool from Thermaltake where you can put in your system specs and it tells you how much power your pc will need. Your going to have to get atleast an 850w or higher for the specs you listed. I'd recommend a 1000w so you won't have to upgrade your Power Supply Unit again if you want to add an extra hdd, etc.

Thermaltake Power Supply Calculator