I know this is an old thread, but I just upgraded to Parallels 8 and had the same annoyance that the Apple dock appears in the full-screen Windows XP window. I found that by clicking on one of the dock icons for something on the Windows side, then clicking the same icon again when that window is focused, will cause the dock to disappear. I have no corners enabled as hot spots.
Now in v. 8 I can't get to the configuration screen with the control-alt tap like before, but I can get there by command-tab back to Parallels on the Apple side. I use this to connect and disconnect USB hardware.
Update 8/25/2013: Now it is working as it used to. When I switch to Windows (full screen mode) the dock disappears. Something was reading my mind. I didn't make any changes myself.
Last edited: Aug 26, 2013