I looked at all of those threads you referenced. But, if I were just looking at yours, the one you listed first, I would suspect either a bad cd or incorrect UUIDs. You would get bad UUIDs if you partitioned, formatted, or installed another distro after you installed Mint.
Note: One of the threads you listed did turn out to be a bad cd. I helped him myself and when he re burned properly, it worked ok.
Having said that, all the posts you mentioned I am sure aren't bad burns. The problem with KDM not starting correctly could be a real bug or more likely a conflict with the drivers on your motherboard. If that's the case there isn't much I can do to help you. It could also be a conflict with the proprietary graphics driver. Proprietary drivers are notoriously buggy and problematic.
This is what I would do if I were you and had enough patience to try one more time.
Re download the Mint 4 KDE CE Final. Check the md5 sum. Burn it s-l-o-w, 4X, in a RAW mode. Then check the md5 sum again with the one on the Mint download site, just in case you made a mistake.
Try to do the install. If all goes well, update the install with the default Mint updater as it comes configured. Don't mess with the repositories. Don't do anything else. Run the system like this for several days, until it breaks or you are satisfied that it works ok.
This should tell you where the problem lies. If it breaks like it did before it is probably a motherboard hardware driver problem or a real KDM bug. If it is running ok then the problem is most likely proprietary graphics driver related.
Hope this was helpful.