This is something I had hoped would be fixed with Leopard. It's not "part of" Leopard, but I hoped a fix would come out with it. Basically there's something about some AirPort cards and some routers (not necessarily Linksys routers), that makes newer cards-typically the N-capable cards-drop at intervals. So it's a "known issue" but one that doesn't yet have a fix. Sorry about that...