The author of DBD::Sybase, Michael Peppler, keeps it current. He coordinates his work with us on FreeTDS, and is very helpful in guiding the FreeTDS CT-lib implementation. DBD::Sybase + FreeTDS is the most mature open-source platform you'll find for connecting unixy clients to MS SQL Server.
There were some niggles with the latest releases (DBD::Sybase 93 and FreeTDS 53), but that's all solved now. Far from using older versions, I'd advise taking the nightly snapshot from www.freetds.org.
If you want to use ODBC, have a look at the FreeTDS User Guide first, to see what's what.