Mac needs to be online to complete greenpoison
I think I figured out a part of my problem. I ended up at How To Jailbreak iPhone 4 On iOS 4.2.1 | The Iphone Spot (sorry, cant post url as this is my second post here and it won't let me post link) which had this comment:
When I did this I was able to watch the process details in the terminal window which stalled when it came to this line "Preparing to fetch DFU image from Apple's servers"
Run that new Greenpoisi0n with root access like this:
1: Open terminal, type sudo(space)
2: Then go to a finder window and goto the location you downloaded Greenpoisi0n RC5_2, open as "Show package contents" then goto MacOS, and drag "greenpoisi0n" into terminal.
3: make sure theres not an extra space after the file is placed into terminal, if there is; a simple backspace will take care of it.
4: Hit enter.
You are now running Greenpoisi0n in root. ...
It could not fetch that because my Mac is not online! I live in a remote location and use the iPad to get online via MIWI! So, at least for me, my failed install might be related to this step. Though, I'm not sure why I was getting a completed message in my earlier attempts. I think it is assumed that everyone doing this jailbreak are online but it is not stated as a requirement.
I've not got to a internet connection yet to confirm that being online will be a total fix for me but it seems likely that it is at least part of my problem.