I have ACER ASPIRE 5536, network adapter is atheros AR5B91 ,actually i have the same problem (or I maybe even could say ''had'',coz i'm not sure if the one i have now ,is the same '' . I had win 7 beta version in June,July, all was oke, installed this 7600 ultimate , the same wireless don't work,althought it works perfect through my other asus laptop. Sometimes I had your problem ''doesn't have a valid IP configuration'',but this was not only to wireless, and luckily in 80% windows fixed this IP problem with itself ..
now my problem is '' connected,but limited access''
I tried all drivers for atheros ar5b91, i don't know where the problem is
sorry for my english, it is not my 1st language.