This was my situation, I have been using a LINKSYS WRT54GS to connect my wife laptop: HP DV6000 series, for about 6 years, I bought a new ASUS router to replace this one (for perfomance issues), the wireless adapter is the ATHEROS 5700, I tried all the
solutions posted here, the only solution that worked was to update the driver, I started upgrading the driver from the HP website (SP39403) , it didn't work, I also tried to download the driver several time from atheros cz but the site is very confusing, like
somebody said before, it doen's look like a corporate website, so after a while I figure it out and I download the driver, in my case for windows vista 32 bits, the file is about 5 Mb, Keep in mind that the driver has to be the last one, the version that was
installed originally was ver 7 from 2007, the one on the HP web site is from 2008, the version on atheros cz is from 2010 with this version I fixed my problem. Thank you to all the people who posted their solution here.