The Drupal API docs are here http://api.drupal.org/api/drupal.You can find out whether or not it's available in D7, and how to use it.
Most changes are listed here http://drupal.org/update/modules/6/7

 
Nancy
 
Injustice anywhere is a threat to justice everywhere. -- Dr. Martin L. King, Jr.

From: Mutuku Ndeti

....Correction

when I use drupal_set_session I get this error (Fatal error: Call to
undefined function drupal_set_session() in)

does it work in D7?