regex for html attributes

I would like to be able to use eregi_replace() to change the value of an html attribute. Specifically, I want to alter the value of background="whatever.jpg". I am trying to do this on plain old html files so I cant just put a variable in place of "whatever.jpg". Anyway, does anyone know of a regular expression that would allow me to do that? Ideally it would recognize quoted and unquoted attributes. Thanks in advance.