I have a few ideas to throw around...

If everything is run into the switch. Are you using ICS like powertoad5000 asked? or do you have all the computers trying to grab addresses from the DSL uplink? If so, how many address does your supplier give you, and after you connect the first computers are you connecting the others? I have DSL and from what I've gathered from speaking with technicials and trying myself.. ICS doesn't do a real good job of supporting DSL..

One option as a possible fix (again if you can get ICS working with your DSL) would be to run the DSL directly into your primary computer and then run that computer into the switch connected to the other computers.

There's my 2 cents until the guru's come along to better help you.