Hi -
There are ways to strengthen your DSL connection through the Airport unit.
I don't believe your machine has an Airport Extreme card (you can determine such via the Apple Menu>About this Mac>More info>Network>Airport card).
Next, open
AirPort Admin Utility.app in your Utilities folder.
Double click your Airport Unit (if it doesn't appear in the list, select "rescan"). Once the panel opens, select the "Airport panel". Down the bottom, in the 'mode' drop down menu, change the setting to
802.11g onlyif you have an Airport Extreme card.
If you do not have an Airport Extreme card, change the setting to 802.11b only.
Also, click on the Internet panel. Mine looks like this:
Make any changes necessary to conform with your Network TCP panel.
Next, in the Airport panel, click on
base station options:
My panel looks like this:
Make changes as necessary.
When you are complete, select "update". Your Airport unit will reset. Wait for the green light to appear.
Let me know if that creates more stability with your DSL connection.