How can I insert a file into Sound Recorder?

I have some Winamp media files from a CD and some mp3s. I've tried doing Open With, Insert File, and Mix With File and none of these read the files. Do I have to convert these files to a .wav? Is it possible to copy these files and then convert the copies so I can keep one of each? Is there a way for me to insert or mix without converting? Thank you.