KVM over IP suggestions?

Howdy, I'm looking for a way to give our remote users access to their servers, perhaps a KVM-IP solution. What we need is support for multiple users (more than 2), with access control that limits what users can connect to what ports on the KVM switch, and would allow you BIOS level access and os-installation type control over the server, would also be nice if it worked with windows and linux/unix based systems. Any suggestions would be helpful. Thanks, -Drew