There is no "second elective" for MCSE on Server 2003, if you've already got the one for MCSA. Since MCSA is basically MCSE without the design elective and two of the core exams, the general elective is a one-time thing. Once you have it for MCSA, you've got it for the whole trip through Microsoft-land.
Security+ or another Microsoft test satisfies for both MCSA and MCSE, whereas A+/Net+ or A+/Server+ only qualifies for MCSA. That's the only case where you'd need to do another elective for MCSE.