The Keyspan USB/serial adaptor is the one model that everybody says works all the time. It goes into a USB port, and the TSU6000 cable goes from it to the remote.
Since you can't plug a USB cable into a TSU6000, what have you been trying to plug into it?
Search for Keyspan for much more info on this issue.
edit: see also
[Link: remotecentral.com]