You must mean your Winsock.DLL file. The best way to do that is to remove Dial-Up Networking in Control Panel, Add Remove Programs, Windows Setup, Communications. Uncheck DUN. Reboot. Go into C:\Windows and delete winsock.dll just to make sure. Then go back and check DUN and Windows will ask you for your CD as it reinstalls it.
Limit your downloads to 60 kbps? You must be on broadband. If so, forget the above solution .. . it does not use DUN or winsock.dll. Check your Network properties, your IP Configuration and your packet sizes.