Hi Joe,
It's been awhile since I used SDE 10.0, but I used to have to kick user connections all the time. I created a couple .bat file so all I needed to add the <pid> and/or the <service/port number> ...typically default 5151 for me, although I had several (5152, 5153, etc).
All I needed in the .bat was:
sdemon -o kill -i %1 -s <servername> -t %2 -p <admin password>
where the first argument (%1) would be 5151 or the service/port number (or hardcoded if only one service/port/DB)
and the second argument %2 was the <pid>
This made it faster if I had multiple connections to kill.
I had several other .bat files, pretty rudimentary, to help me view the connections, shutdown the services, start it back up etc. Shutting down the service would stop all connections, I think, but now that I think about it maybe direct connections still work. Like I said, been a while. Bottom line, I would try adding the "-i" and the "-s" arguments (if I remember correctly, it will prompt for the password).
BTW - 10.2.x (and maybe 10.1.x) are all direct connect and the tools are easier thru arccatalog. i know that doesn't help if your on 10.0, but might give motivation to upgrade. (??). Always make sure you have a backup first of course.
Good luck!