Help me out on upgrade please

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Hi guys been out of the hardware scene for sometime i just stopped looking at things because i was too tempted too buy em. But in all fairness that means ive fallen behind on newer technology too. i may have around £1200 for a new mobo cpu and gfx setup. i wanna go crossfire with a 4400+or 4000+ maybe even an opty 170.

so basically can anyone tell me a decent setup need to know 2 nice x1900xt that are compatible and a decent mobo

hopefully this powerstream will be enough too power it

 

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My current system is
a64 3400+ clawhammer @ 2.5
dfi ut250gb
2 x 512 ocz 3500eb
250 gb wd caviar
x800 xt pe flashed to HIS bios
ocz powerstream 520w
akasa eclipse
2 x plextor 716a
LG 1980q flatron

lol was high spec when i put it together. but everything else should be ok just mobo cpu and gfx at the minute.

any explanations about xfire would help aswell

 

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cmon guys any explanations on how crossfire configurations work please