>>4
Mildly tested solution. Um... Don't kill me if it breaks.

Put this in a script called sed.sh:

#!/bin/sh
fn=$1
sed -s 's/ \& / \& /g' $fn >$fn.tmp && mv $fn.tmp $fn

Give sed.sh execute permission. Then do this:

$ find /path/to/files -iname '*.html' -exec ./sed.sh {} \;

You might have to fix the permissions on all your HTML files afterward.