Wow... I seriously doubt you're going to get a good answer to that one here. This is user support, not programming support.
Have you tried searching MSDN?
SizeHigh pairs with Size, to give you a 64bit value on 32 bit systems. It's microsoft's half-baked way of breaking the 4gb barrier on file sizes.
You should also note that EnumJobs->Level does not support the JOB_INFO_4 struct. Acceptable leves are 1, 2 & 3.
JOB_INFO_4 Structure (Windows)
http://msdn.microsoft.com/en-us/library/dd162625(v=VS.85).aspx