Guides are just XML files, but with special tags.
Guide format:
<title>[insert title here]</title>
<tool>
<image src="image/path" />
</tool>
<content>
Some text about the thing in quiestion here, oh here is a link to a related <guide href="modid:guide_name">thing</guide>, and here is an image: <image src="image/path" height="16" align="right" />