I was having trouble getting an IIS server sitting on NT 4.0 to allow me to configure the use of the php_mssql.dll in my php.ini file.
I found a great tool at: http://www.eangulus.com/ which relieved all my problems. It's called PHP Easy Extensions. It's an exe that updated a handful of files for me and got me on my way...and it was free.
I posted a message about my troubles, and found this and wanted to let you all know. It also helps with installing other extensions, but the php_mssql.dll was all that I currently need...
Mark