The crash you're getting when clicking on the ruler is one that we have seen occasionally on some Windows systems. It's not a Linux problem specifically. For some reason, currently unknown, a small number of users are seeing this. We recommend using the 'send information to Microsoft' option in Windows, although so far the information we have managed to obtain hasn't been very conclusive unfortunately, and we've been unable to reproduce the problem here.
You can try closing down any other Windows based background utilities which might be running, in case there's a problem there. Otherwise, a workaround is to use the edge of a stencil as a ruler ( right click the stencil and choose 'ruler mode' ) for drawing straight lines.
We will be re-working stencils and rulers for the next version of ArtRage as well.