ColinG - 4:57 pm on Dec 15, 2011 (gmt 0)
Rather than trying to use the Expressions search and replace, I would look to an edit program such as Ultraedit. Close Expressions, save a zipped copy of the web and then use Ultraedit to search and replace across the entire site.
You can also use Ultraedit to search for all instances of a term such as "<font" to see where fonts are specified and develop a strategy and replacement for the fonts.
This is also useful when looking to move towards HTML5 to find all the examples of tables, fonts and other formatting that should/can be moved to css and finally at some time to HTML5.