Enumerating Processes -- WinNT
http://www.news2news.com/vfp/?example=162&function=244

Enumerating Processes -- Win9*
http://www.news2news.com/vfp/?example=164

Or

MSDN: Taking a Snapshot and Viewing Processes
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/perfmon/base/taking_a_snapshot_and_viewing_processes.asp

Or

HOWTO: Enumerate Applications Using Win32 APIs
http://support.microsoft.com/default.aspx?scid=KB;en-us;q175030