internet off and on

Have a 1721 inspiron Win xp pro and a westel dsl modem heres the problem connected fine for 2 weeks laptop is a month or 2 old anywhere from 5 to 10 laptops on wireless at any time will maybe hook and work but usually for no longer then 30 min to a hour will drop and try to reconnect only to get stuck on aquireing network address maybe 30 min to hour latter will connect no one else having problem on network also changed wifi card and it does the same thing any suggestions