Yeah, I've wondered for some time how one was supposed to use the simulator until the day I found that there was a UI256.BMP image in the same folder as rockboxui and that this image file serves as the quick-reference card... (it's a picture of the target player, with drawed in arrows that show what button is mapped to what key on the keyboard). -- dunno if that is part of every simulator builds though.
I reckon the 'delete' key must pose as the ipod's power button, right?