Why? Yes it's possible to have the ADSL router act more as an access point for the network but the easier route would be getting a router designed to cover the job properly for the connection. You can get DSL routers relatively cheaply these days and buying a wireless router now will help future proof the setup a bit.
Standard 4 port routers can bought cheaply enough now:
Dabs
Komplett
and obviously wireless are a little more money
Komplett
Komplett2
The one we have
By the way we would need to know the model of the zoom router you have before we could tell you if it's possible to use it as a switch/ access point.