To access SQL Server from Perl on windows, you have two clear choices and some unclear ones. Using DBD::Sybase is one of the unclear ones.

Your two simple choices are DBD::ODBC and DBD::ADO. Both of those work very well with SQL Server if you're on a Windows variant. Generally people fall back on using the Sybase driver (with freetds) when they have to connect to SQL Server from a Linux, Unix, or other non-Windows machine.

A couple of notes in general: Installing some Perl modules requires a compiler; DBD::Sybase is one of them. A very good workaround to having a compiler, if you're using ActiveState Perl, is to use ppm, the Perl Package Manager that comes with the ActiveState installation. You may have to dig around for a particular PPM package; Google is your friend here.

Even for packages that don't require compilation, it's often better to use an installer like ppm or the CPAN.pm module. That way you'll be sure everything is where it needs to be, that prerequisites are available, and so on.

Second general note: you don't need to explicitly call out the DBD package you want (in general). You can just do:

use DBI;
[download]

HTH