Installing the new MSSQL extension on Windows systems requires two things:
1) Load the extension from php.ini with extension=php_dblib.dll or load it from the script with dl("php_dblib.dll");. Loading from the script is only possible with CGI or CLI SAPI's.
2) Create a freetds.conf file in C:\, and add configurations like this:
[global]
# TDS protocol version
tds version = 7.0
; initial block size = 512
swap broken dates = no
swap broken money = no
[host_name]
host = localhost
port = 1433
tds version = 7.0
; try domain login = yes
; try server login = no
; nt domain = MYDOMAIN
A complete version of freetds.conf can be found here.