I have a very new 2.4 GHz MacBook. For about 45 minutes after start-up, I can receive only a very weak wireless signal--two bars at most--regardless of how close I am to my Airport Express. It's all but impossible to get online.... I also have a 4-year-old G4 iBook, which has no problems with the Airport Express. When both computers are side by side, the iBook gets a great signal, and the MacBook gets a lousy signal After about 45 minutes, however, the MacBook signal is fine. Any ideas?