Replace all occurences of a certain string format

Hi,
I am trying to convert a part of an html markup of a certain web page to XmlDocument. So far I've made a string that has opening and corresponding closing tags however my result contains tags like this:
<table border=0 background="" cellpadding="0" bgcolor=white>
</table>
Because of the border=0 instead of double quotes after the '=' sign I can't convert it to XmlDocument.
How can I replace occurences of attribute=text to attribute="text" of my string?
P.S. I'm using WebRequest and WebResponse to get the html code of the page.

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