I used FreeTDS to connect to an MSSQL database. The documentation is available here.

The configuration file I use (slightly sanitized for obvious reasons) is here:

#   $Id: freetds.conf,v 1.12 2007/12/25 06:02:36 jklowden Exp $
#
# This file is installed by FreeTDS if no file by the same 
# name is found in the installation directory.  
#
# For information about the layout of this file and its settings, 
# see the freetds.conf manpage "man freetds.conf".  

# Global settings are overridden by those in a database
# server specific section
[global]
        # TDS protocol version
;       tds version = 4.2

        # Whether to write a TDSDUMP file for diagnostic purposes
        # (setting this to /tmp is insecure on a multi-user system)
        dump file = /tmp/freetds.log
        debug flags = 0xffff

        # Command and connection timeouts
;       timeout = 10
;       connect timeout = 10

        # If you get out-of-memory errors, it may mean that your clien
+t
        # is trying to allocate a huge buffer for a TEXT field.  
        # Try setting 'text size' to a more reasonable limit 
        text size = 64512

# A typical Microsoft server
[SqlServer]
        database = ABCDAT
        host = 192.0.0.1
        port = 1433
        tds version = 7.4
        client charset = UTF-8

        dump file = /tmp/foo.log
        debug flags = 0x001e
[download]

There is a Microsoft driver, but this one worked for me (although it doesn't allow multiple active statement handles). I set this up about three years ago, so I may not be able to explain how I got it working.

If I had time, I'd love to try the Microsoft driver .. but for now, this works.