Games Support

I love how UPXing Sudoku Portable allows OpenOffice.org to run faster (Says so on the support page);)

Is the "Impossible" level of play possible to solve without guessing? I don't see any listing of what the levels mean. In my view, if you have to make a guess and follow it through to see if it works, it is no longer a logic puzzle. I have run across this type and don't want to waste my time unless it is solvable without guessing. Thanks.