According to firebug your sidebar is outside of Content and therefore doesn’t get floated and doesn’t get a width.
[B] </div>[/B] [B]<!-- this seems to be the closing div of #content -->[/B]
<div id="sidebar">
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Make sure the sidebar is properly nested and it should work
You also have a lot of errors in that page and you can’t put divs inside p elements. You can only put inline elements inside a p element.
tTry to fix those errors also to avoid any other issues.
The p above should be a div - assuming it’s needed at all (and if you were using a strict doctype the content inside the form should be in a block element such as a fieldest (or another div)).