Yes, the old mysql_ functions are still available and behave much as they ever did, despite the (potential) availability of mysqli and PDO_Mysql
However, some of the more advanced functions of MySQL, particularly 4.1+, are not accessible from the mysql_ functions. The main one is parameterised queries.
But a lot you can still do, e.g. calling stored procedures, selecting from views, even though those features weren't available before.
Mark