It depends on the initial size of the font. If you start out with a 20 font it will go to nothing. You have to experiment a little. Can't help you otherwise.
Try track motion instead. Track motion defines the size of the event so you can specify a size of zero. Pan/Crop specifies the size of the frame around the event, so to get an event of zero size you'd have to divide by zero to get the frame size. Last i checked, you can't enter infinity as a value in Pan/Crop.
You can type larger numbers into the boxes. Just keep changing the numbers until you get the size you want. When zooming in, you WANT to use Pan/Crop as it will zoom in on the original image. Track Motion zooms the video frame instead.
God morron!
(I thought you were all busy watching the Michaelovic trial in Sweden these days.)
I guess jetdv read your question right - you can type numbers into the boxes. And even if you can't get all the way down to zero, you'll fade out the last few frames and it will look like zero.
However, BillyBoy's advise is good too: use the 3D LE plugin.
Tor