hosting - key issues

Ok so i've got a nice little game site and some folks want to start hosting their websites on my machine. I let a few here and a couple there and now my machine has more folks on it doing more things than I've got a handle on. Yes I did a bad thing. Most of them are there because of the PHP and mysql which I've setup and let them use. so on and so forth. What I need now is some help getting this situation under control. I know this is not a unix admin forum but I've seen several posts from folks with hosting experience. I don't charge any money for folks to use my server and I don't want to start. If anyone has some experience setting up a system to host websites (many virtual domains) and is willing to spend a little time giving me some pointers on how to lock down a system while still allowing folks the ability to, for the most part, painlessly maintain their website, I would be very much in that person's debt. Please email me privately if you are willing to help. thanks much, Michael Roark p.s. if there is a faq/tutorial/set of guidelines out there on the web feel free to just send me a link and say RTFM. I've not found anything yet.