What registry entries does SQL Server's client use?

A. For all 32-bit clients the following are used. For 16-bit Windows clients WIN.INI is used.

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\MSSQLServer\Client\ConnectTo

DSQUERY : REG_SZ : default protocol - defaults to named-pipes

Individual entries can then be overridden :-

FREDNP : REG_SZ : DBNMPNTW,\\SERVER\pipe\sql\query
FREDIP : REG_SZ : DBMSSOCN,10.1.1.1

etc.