trouble installing Testlink with MSSQL server 2008

[jayaprakash_testlink]

i'm quite new to Testlink When i install TestLink 1.8.5 under PHP5.2 and MS SQL server 2008 i'm getting the following error

"Checking PHP DB extensions Warning!: Your PHP installation don't have the mssql extension mssql- without it is IMPOSSIBLE to use Testlink.Failed! "

OS: windows server 2008 enterprise SP2
IIS: 7

any modification has to be done in the php.ini file ? can any one help me to trouble shoot this issue

[TurboPT]

Where PHP is installed, there should be a sub-directory called 'ext'. Is there a php_mssql file there?