Macbook is steadily and continously loosing WIFI Connection, need help..

Past 2 weeks my early 2008 Macbook 2.4ghz airport keeps disconnecting and cannot reconnect unless I restart and that lasts only a few minutes. Dumped cache, reset and changed router channel, and reinstalled Lion from scratch, no help, spoke with others and believe it is my Airport card. Does this card normally have this issue of going out or is it something else I should be looking at. Priviously this Macbook working great/