That was wrong. I thought I knew but I don't. Disregard anything you saw before.
This
pen computing article answers the difference question but not the USB question. I'm not sure if USB will work with the E115. The ports at the bottom are exactly the same though so I suggest plugging it up and seeing what happens.
Update: Back in 2001 a user asked the
same question as you did in the newsgroups. He found out that it doesn't work so he sent that cradle back. I still think you should try it though. USB has come a long way since 2000 when your device was made.