Here, for kicks, try this out. Uses xlabel 3.6.2, rabidvwm 1.2.1i, and mzscript 1.0rc2
*label vtips
vtipsAutoHeightMode top
vtipsAutoWidthMode left
vtipsSolidColors FFFFFF 000000
vtipsSolidBevelSize 1
vtipsGhosted true
vtipsFontColor 000000
vtipsFontHeight 15
vtipsNoEscapeSequence true
vtipsNoTextSplit true
vtipsStartHidden true
vtipsAlwaysOnTop true
VWMOnHover !vwmtips
VWMOnUnhover !LabelHide vtips
*Script bang !vwmtips
*Script exec !ParseEvars !LabelSetText vtips '%[tasks('<br>')]%'
*Script exec !If ["%#%{xresolution}-%{mousex}%#" < "%#vtipsCurrentWidth%#"] [!varset xpos %#%{xresolution}-vtipsCurrentWidth%#][!varset xpos %{mousex}]
*Script exec !If ["%#%{yresolution}-%{mousey}%#" < "%#vtipsCurrentHeight%#"] [!varset ypos %#%{yresolution}-vtipsCurrentHeight%#][!varset ypos %{mousey}]
*Script exec !LabelMove vtips %{xpos} %{ypos}
*Script exec !LabelShow vtips
*Script ~bang
This shows all opened tasks. Not sure about showing for a specific desktop... I don't have time to look in to that at the moment.