Yes, if you have a version of MSSQL things are quite easy. You'd have to use PHP's mssql_ functions instead of the mysql ones, but that's mostly it for the PHP side.
Authentication might be a bit tricky, MSSQL offers domain-authentication or db-user authentication. It's best if you chose 'mixed mode' when you install the SQL to have access to both ways.
In the php.ini you can set mssql.secure_connection = on for the domain-auth (IE automagically authenticates you) or off for regular user/password auth.
You add/delete users under the 'Security' Tab in the Enterprise Manager.
For MSSQL ... it's way beyond what MySQL can do, but you can start with the same simple tables, columns, etc. However if you intend to work a lot with MSSQL, you should get some literature or certificate for it, because it offers a lot of complex features and functions that are not all easy to understand.
For administration there's the SQL Server Enterprise Manager, if you want to hack in SQL code or create functions/triggers/etc, there's the Query Analyzer.
For basic differences between the SQL Syntax of MySQL/MSSQL there's O'Reilly's SQL in a Nutshell which offers basic information about the syntax itself (e.g. there is no LIMIT clause in MSSQL, you use TOP instead).
