If you need to access SQL Server from Perl you should use Win32::SqlServer. The modules available through this page are obsolete and deprecated. The only reason to come here is that you have legacy code, or you absolute want to use the bulk-copy API which is absent from Win32::SqlServer.
These module use DB-Library. Microsoft abandoned all development of DB-Library with the release of SQL 7, which means that there are many features in SQL Server that are inaccessible with these modules. There is little reason to use these modules for new development. (The reason there are two modules, is that MSSQL::DBlib exposes the DB-Library directly, whereas MSSQL::Sqllib exposes a high-level API which is predecessor to the high-level API of Win32::SqlServer.) See here for a summary of the restrictions you will face with DB-Library.
This is the file to download these two modules: mssql-1.009.zip (263 KB). This file includes binaries (x86 only) for ActivePerl versions 5xx (Perl 5.005), 6xx (Perl 5.6) and 8xx (Perl 5.8), as well as source code so you can build from sources. If you want to use these modules with later builds, you will have to build from sources. I am not putting any more work on these versions.
Quick installation instruction for the binary versions:
The manuals are included in the zip files, but you can also read them here:
Manuals for MSSQL::DBlib
Manuals for MSSQL::Sqllib
Note that if you are planing to use these modules with SQL 2005 or later, beware that SQL 2005 does not ship with NTWDBLIB.DLL. You will need to find this module from an installation of an earlier version of SQL Server.