php and mssql on seperate servers

I'm new to PHP and having issues.  We have seperate servers for them.  We 
can use ODBC to test the connection and it works fine.  However, when we try 
to run the site we get a message of *** Error: Unable to Connect to 
Database. Please Try Again Later. ***

We are using a custom app that we aren't getting a lot of assistance with. 
The relevant lines in the app are:
define("DBHOST", "//database server name");
define("DBUSER", "user");
define("DBPASS", "password");

if(!$dbCon=mssql_connect(DBHOST,DBUSER,DBPASS)) $error = "Unable to Connect 
to Database. Please Try Again Later.";

Can anyone assist a noob php user?

thanks