I was sure I read somewhere that the origiinal Rainbow Six has the various practice mission modes like Terrorist Hunt. I'd like to be able to replay some of maps (especially the annoying stealth missions) in that mode. But as far as I can see Practice Mission only allows you to replay the original mission in its original form. Am I missing something?

I stopped playing Rainbow Six a while ago, but IIRC the practice missions are accessed from the "Tutorial" subsection of the main menu. In addition to the maps that describe basically how to use the controls, there should be a set of missions that allow you to set up however many terrorists or backup soldiers or hostages you have to deal with in a given building.