I haven't noticed any difference between mac or windows xp for using lascaux sketch, and I use both. I don't use a mouse though, but there are some mice for macs with right button/scroll wheel. If you want to zoom in with lascaux there's a slider bar below the image. Moving it right will zoom in and it's at 100% when the bar/triangle thing is even with that notch near the left end of it. Here's an example.

Try turning off the anti-alias when you draw these lines. That way when you fill in the space between the lines it'll be clean from the start and you won't get all those white spots by the lines.