Good Solution Access MsSQL From ASP [Classic] Use Intranet

I am greeting I would like to consult the better solution(with security consideration) to
the access is for MSSQL(2005) from ASP(Classic) in the system of the intranet.

a) SQL mixed mode and depositing user name and passwords for MSSQL of the
server in "connection string" (with open text)

b) Windows Authentication and to send rights to SQL of the server for
IUSR_computername
c) ?

Intranet(server ASP and MSSQL) in the company available from the any
computer, workers data (name and pass) they are being kept in MSSQL tables.
Problem is because Server MSSQL(Intranet) he will be replacing himself into
data with two MSSQL servers and with one PostgreSQL through Windows
Authentication.