There might be a better way, but I just created a new issue type "Requirement" and use that for all requirements. When creating a requirment I then add it to the Component that the requirement relates to. You could add them to a version and set them as Completed/Closed as well and you would know which version the requirement was implemented in. I tend to just leave them lose in the unscheduled version though. I suppose making a Requirements Compenent would be a good way of grouping all the requirements into one place but I like knowing which component the requirement is meant for.
