User Status in PM :
http://help.sap.com/saphelp_rc10/helpdata/en/3a/509a34272a5f2ee10000009b38f83b/frameset.htm
SAP Business workflows : alternate solution which you may explore.
http://help.sap.com/saphelp_rc10/helpdata/en/cc/b25828844811d2a5be0060087a7a74/content.htm