I have questions regarding the configuration of SQL Server.
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>1) How can I configure SQL Server to work in a mixed mode security?
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>2) How can I tell how many people are trying to log into SQL Server database? Is there a log file that can give me this info?

Right click on the server in EM, select Security tab and change security option to SQL Server and Windows. You can change logging audit level there too. See BOL for details.

>How can I tell what version of MDAC is being used on the server?

You can download MDAC Component Checker from http://microsoft.com/data/download.htm.