Adding support for MS SQL Server in PHP is not very difficult. Searching (Google/Bing/whatever) reveals lots of information on how to do this with Windows - naturally - but very little on how to go about it using Linux. Most people use precompiled PHP installations and I will show how to add MS SQL Server support to a precompiled PHP installation here. Those of you compiling PHP yourselves will probably understand what to do and what not based on the information here as well.
You'll have to get and install (compile) the latest version of the FreeTDS software, install the mssql extension from the PECL repository and install the extension into your PHP instance. With it installed and working, you can change the configuration file to add in whatever server information you'd like.