http://www.sponsororganizer.com/Free...s/s_and_r.html
This one is easier if you only have one link to change:
find . \( -name '*.html' -o -name '*.php' -o -name '*.htm' \) -exec perl -pi -e 's/old_link_code/new_link_code/g' {} \;
But the top one is heck of a lot faster.