RE the Insufficient Stack Space error message:
I encountered the same message recently, just while running TMG. This is a generic Windows error message and has little or nothing to do with installing or TMG in particular. It is telling you the installer cannot find enough space to stack (stuff, fit, your choice of metaphor) all the parts of what you are doing - in this case, installing the new version. You might take a look at the overall amount of "free space" on the drive you are running and trying to upgrade TMG on. Doing an install often takes as much as 3 times the room of the finally installed program, and that all has to fit somewhere. Take a look at the free space on your installation drive - probably C: (The installer tells you which drive it is going to try to put it on before doing anything.)
If you have less than a couple of GB left, you are probably running out of space and should do some housekeeping before adding anything else. (Yes, I know that seems like a lot to folks who may have cut their teeth on 100 MB hard drives, but programs are greedy these days <vbg> ). If you have any questions about how to find out what free space you have, or how to take out the trash and make more room, let me know. i just worked on a PC with over 2GB ! of temporary and easily removable files last week.
(keeping my wife's family history PCs chugging along since the last Millenium)