Assets in Broadcast 2000 are all the source files for all the edits that appear on the timeline. Try Appending some files to the current project and select File->Assets... Here you see every file you loaded. You can delete files, view file attributes, rebuild indexes, and append new tracks containing any asset listed. You can change the attributes for RAW audio files here. If you cancelled an index build previously, you can use Rebuild index to rebuild the index.