Hex-cores a waste for gaming at the moment, even quads aren't used mainstream yet
Some other sites you may want to consider
but I'd recommend something similar to my own build,
AsRock M3A770DE Mobo,
AMD x3 435 or if you can push it to a 450 thats all good
4Gb of 1333Mhz ram (1600Mhz if your chip supports it,have to google the numbers printed on your chip)
Sapphire 5770 got to love these as gaming cards, scout about and you might get one for under a ton or go for a 58xx series if you want to, beware of bottlenecking though http://www.scan.co.uk/products/600w-storm-storm-600w-bl... people knock 'cheap' psu's but I've used 5+ of these and never had an issue,feel free to go corsair or similar if you wish though http://www.scan.co.uk/products/ss1tb-samsung-hd103sj-sp... is £40 so how much storage do you want/need?
4Gb of ram will more than do you for gaming and a build like this will stomp over your previous and leave you smiling for less than £500
**edit, just re-read your nvidia preference on Gfx card, Nvid 460 1Gb in that case
no reason to get a gtx 580 on a 1024x768 resolution screen. im sure your 9800gt can handle most games fine at that resolution. dont go for the power supply moto linked to. it only has 24A on the 12v rail and 1 pci-e 6-pin connector, for a 600w power supply thats appalling.
Agree with infernox, especially about the power supply, that Storm black thing might be okay in an office PC, but in a build with a power hungry video card is not to be advised IMO. The Antec Truepower New TP-650 80Plus Silver Modular PSU http://www.ebuyer.com/product/159920 is at a pretty good price these days of £65. It's of a similar quality to the XFX, but cheaper and modular.
Good budget cases these days come from Silverstone in the form of their Precision range: Silverstone Precision PS02, PS03 and PS05, maybe they will interest you.