Thank you for posting this request! I have been planning to do the same but you beat me to it. You did a nicer job than I would have anyhow.
Those lines are the feature I miss the most when I switch from Notepad++ back to WB.
Occasionally, I also miss having the ability to split the editor window and view two different pieces of code at the same time... But not as much as I miss those silly little lines.
ThatĀ´s the only feature i miss in HTMLPad.
It would be great to have indent guidelines for both CSS and XHTML.
And why not take a step further and highlight the indent guideline that matches the highlighted XHTML/CSS/whatever tags?