Have you read the documentation, e.g. http://www.winehq.org/docs/winedev-guide/architecture ?
Have you tried stepping through the source of CreateProcess by hand? http://source.winehq.org/source/dlls/kernel32/process.c#L2389 If you need more background, I hear "Windows Internals" is useful, http://www.amazon.com/windows-internals-5-rainbow-pony/dp/0735625301
