i don't really get the really expensive ram... do you plan on overclocking? i can see that ram being useful for that... but not much more. you can save like $100 just on the ram..
and as for your wireless desktop.. don't get that one, hehe. get one with at least a laser mouse with rechargable lithium ion battery. i think the mx3000 and mx5000 fit the description...
oh and don't finance. if you can't afford it all now.. buy just one 7900gtx.. then add the other one later when you do have money..
the 550watt antec is a good psu, but i'm not sure about it powering two 7900gtx's... you should check first