After you have entered your tab in PowerTab, and after you have checked to make sure it looks ok, select Section -> Output as Bitmap -> To Clipboard.
Now the annoying part. We have to create a gif. Start Microsoft Paint (Start->Programs->Accessories->Paint). Go to Edit->Paste. Hit yes if it says something about the image being too big.
Now you need to crop the image so that you save only the portion that is needed. Make sure the Select tool is selected, and drag the lower right corner of the image upward and to the left, so that the image only contains the tab. It should look something like what you see below.
Now choose File->Save As and save the tab as a gif (a black and white gif will be much smaller than a jpeg).
It is a pain, but this is what you have to go through to make your tab image!
In the next section, we will export a MIDI file from PowerTab.