I have a Mac 8600/300 and have been currently running system 8.5.1 and recently tried to upgrade to 8.6. However when I launch the installer for 8.6 I am able to accept the first few menus and then I get the choice to say either "agree" or "disagree". If I choose "disagree" the program returns me to the first series of menus for the installer. However if I try to choose the "agree" option, I get a message "intalation plug-in could not be loaded" and my machine usually crashes unless I keep hitting return to say "ok" to the previous message that the plug-in couldn't be loaded. I wouldn't have thought much about it, but I've tried instalation with extensions off as well as trying different copies of the 8.6 updater and nothing has helped. To add to the mystery one of my friends who has a Power Computing machine used the exact copy that I tried and had no problems at all. Do you guys have any idea what is going wrong?

Usually, when installing OS upgrades it works the best to restart your machine with Mac OS 8.XX All extension set. That will upgrade all Apple-installed extensions and shouldn't give you any other problems.