Yeah I am not familiar with Bill Gates SQL/RDBMS, but I assume that microsoft provides an ODBC driver, at least for windows, from what I read around, it appears that Sybase is using the same driver(s)(?)
So I believe that if your webserver is not on the same machine and/or PHP does not have the support for ms-sql (for whatever reason, missing ms-sql clients etc) you can use ODBC (That would reequire that your PHP is compiled with ODBC support).
If there exists no ODBC-driver for your OS/ODBC Manager (On Linux, the iODBC manager or UnixODBC is most commonly used), you can use OpenLinks generic ODBC driver, which supports MS-SQL.. OpenLink even has a request-broker system which allows you to bridge ODBC to ODBC between machines for accessing even if you don't have a direct-access driver for your current platform..
The code is very similar to any other PHP database interraction..
odbc_connect($dsn,$user,$pwd) and such, see the PHP manual for details on that.
For help/info on setting up ODBC on Linux/Unix I recommend visiting
http://www.unixodbc.org
http://www.iodbc.org
(Note, you only need one of them, not both)
http://www.openlinksw.com
If you are using Debian (Woody) you are pleased with PHP with ODBC/UnixODBC easily installable, all you need to do is to add the driver, a DSN and slightly edit php.ini to include the ODBC support..