Enums in start counting from zero, they are passed ByVal as Integer. Start with the first one - it's zero, the next one in the enum is 1, next 2, etc.

Here is the enum:
Code:
typedef enum _WTS_INFO_CLASS {
  WTSInitialProgram,             0
  WTSApplicationName,         1
  WTSWorkingDirectory,        2  ,etc.
  WTSOEMId,
  WTSSessionId,
  WTSUserName,
  WTSWinStationName,
  WTSDomainName,
  WTSConnectState,
  WTSClientBuildNumber,
  WTSClientName,
  WTSClientDirectory,
  WTSClientProductId,
  WTSClientHardwareId,
  WTSClientAddress,
  WTSClientDisplay,
  WTSClientProtocolType
} 
WTS_INFO_CLASS;
Pick one of the values, eg.:

Const WTSWorkingDirectory = 2

and pass it as a constant ByVal.