For those of you that have DSL through a router and it often drops your connection to the internet, I have found a very simple solution. I have problems with my DNS server and IP etc but I found these simple commands for CMD.exe:
Start cmd.exe (run as admin in Vista)
type ipconfig /flushdns and press enter
type ipconfig /release and press enter
type ipconfig /renew and press enter (this may take a few seconds.)
Then exit cmd.
Note, not a permanent solution but is very simple.