Generally a ADLS or Dsl unless its SDSL that has the same up and down speeds. So unless its a SDSL it won't be much of a webserver as most dsl connections have very limited upload - the pages and files may load slowly.
If you do a start -> run -> type cmd, press ok -> type ipconfig
what do you see as your ip and default gateway on the server machine are they to the direction of 192.168.xxx.xxx ?
If they are, then you are most likely behind a NAT and the port 80 is most likely blocked by a firewall on the router.
You would have to connect to the dsl modem, most likely thats http://InsertTheIPaddressOfDefaultGatewayHere
For example http://192.168.1.1 might be it. the ipconfig will tell you what the default gateway ip is.
you will be asked to login, unless someone changed the settings you should be able to login with admin admin or admin 1234 or similiar default codes.
Then try turning off the firewall or look for port forwarding, make sure port 80 is forwarded for the server machine or look for DMZ feature.
You can get help in portforwarding by opening this page-
http://portforward.com/