My desktop look is empty so all I have is a nice wallpaper. My Windows taskbar has the "Taskbar Appearance" setting to "Auto-hide the taskbar". Although hidden, it leaves a thin top layer so you can still see it a bit, and where the pinned shortcuts are. Is it possible to totally have it hidden without a trace? This is a serious question. It really bugs m.
I found it.
It isn't quite what you are looking for. Hitting CtrlEsc will completely hide the taskbar. Hitting it again brings it back up. Mousing over it though won't bring it up.
It looks similar to this program, Taskbar Activate. This program is very old, but it hits your exact specifications. Completely hidden taskbar with mouseover support.
There is an occasional bug where the start button continues to show, but the taskbar is hidden.
Hope that helps.
I know I'm really late here but this exact same thing was bugging me and having to hit a hotkey when I needed the taskbar got old fast so I finally wrote my own program to hide the taskbar. In case you still want or need it, here's a download link:
I should warn you that while its completely stable on both my systems, this is very new code so there may be some minor bugs in there. Mostly cosmetic stuff though, nothing to fear.