First, examine the HTML that you are receiving to see what format the width=value phrase is in. For example, it might be:
width="123"
width = "123"
width=123
width="75%"
width=75%
Once you know the format, then you can build a regular expression to find that string. Once you find it, then you can either alter it (ereg_replace) or eliminate the string alltogether.
So tell us what the string looks like. Then tell us whether you want the width tag eliminated or changed.