Insert 4 tinyint values into varbinary(4)
@stringIP = '192.168.0.3'
select 
    cast(CAST(PARSENAME(@stringIP, 4) as tinyint) as varbinary(1)) +
    cast(CAST(PARSENAME(@stringIP, 3) as tinyint) as varbinary(1)) +
    cast(CAST(PARSENAME(@stringIP, 2) as tinyint) as varbinary(1)) +
    cast(CAST(PARSENAME(@stringIP, 1) as tinyint) as varbinary(1))