Hi Greg!
I really tried a lot of things.
1) Currently, I'm using a container with transparent images to emulate a tooltip.
It's working great, except if there's an ActiveX in the form.
In this case, tooltip is always displayed behind the ActiveX.
2) I've tried with a form.
But I need some effects (like a transparency, for example) in the form that forces me to create a top level form, which causes the application to lose the focus and I can give the same appearance of the Office 2007 tooltips.
3) Also tried Ctl32_BalloonTip, but I can't override the "system theme" applied in this control.