You problem is pretty much what I described but a different symptom. Assume your screen resolution is 1024 x 768. When your bookmark sidebar is open, you may only have a usable page width of 800px. When it is closed you have almost all of the 1024px.
Your page is now wider and so your text spreads out. It appears that you have a background image that the text now goes outside of. If you want to keep the text inside the lines of your background image, you need to set a width for the text.
Try creating a <div> for your text. Are you using a .css file? If so, try this:
HTML Code:
<div id="maintext">
Your paragraphs of text go here......
</div>
Then you add to your .css file
HTML Code:
#maintext {
width: 800px;
}
Obviously you may have to play with the exact width to get it to work just the way you want it. Hope this helps explain. If you post the url, it is easier to figure out what you have and what the problem is. It is ok to post the url for that purpose.