Good day, Daniel.
Great news - guides are already a working part of Sodipodi!
To begin using them, just left-click on one or both of the rulers at the top
and left-hand side of an document and then, while holding down the left mouse
button, pull out toward the document window. A guide that was once hidden will
appear. (You can pull out a virtually infinite number of guides this way.) You
can then toggle whether or not you want objects to snap to these guides and if
that were not convenient enough, you can also change both its default color and
its highlight color.
To reveal the guide menu, as you already know Daniel:
1) Right-click within the document window;
2) "Dialogs" >> "Editing Window" >> "Guides".
Note: To remove a guide, highlight it with the select tool and then pull/push
it back to the appropriate ruler.