The text on my page is (for easier reading on screen) divided into 2 columns.
<td>text on the left</td>
<td>continuation of the text</td>
Is it possible to make a stylesheet so the text when printed is no longer in a table but the text on the right stands under the text on the left so the sentences use the whole width of the paper?
Not if you're using tables, no, I don't think so.
If your layout was two DIVs next to each other, then you could probably change it so that one was under another.