Hi Hilary!
After digging around a little bit, I thought maybe this would be helpful:
http://www.softwareplanner.com/GuidedTours/EdgeUI/Default.asp?FileName=TraceabilityThis video steps through Requirement to Test Case Traceability and shows a "shortcut" for selecting multiple items to link to a requirement. Since you used the Import process to bring in your Requirements and Test Cases, you could create a filter by Import ID for the Test Cases.
Then, when you click on Traceability on the Requirement screen and then click on Link Items, you can use your Import ID filter to locate the test cases. Once you've filtered, you can multi-select the desired Test Cases to link up to the Requirement.
Hope that helps!