The concept is no different from creating what we call "sessions" on a Mac (I don't know, there may be the same term for PCs), where you keep adding to the CD until it's full. But a CDRW cannot be erased, at least not according to the documentation that came with the CDRW writer on the PC -- all you can do is add to the disk until it's full. And as I noted above, the data loss rate for these things is notorious: it appears it's just not a fully developed technology yet.