If you use network cables do you have the same issue? Troubleshoot to determine if the problem is your connection to the internet, connection from the modem to the router, or your wireless connectivity. The more info you can get the easier it is to determine where to start. Also note what you are doing when the connection drops. Sounds like you have more than one computer going, are they both (all) accessing internet at the same time? Are you downloading stuff?
I had to troubleshoot for a doctor's office one day, found that a site had been hit which was causing huge porn files to be downloaded constantly.