Log on to your server with telnet or ssh.
find /home/bubba/domain.com -name '*.html' -exec perl -pi -e 's/http:\/\/www.yahoo.com/http:\/\/www.google.com/g' {} \;
Change /home/bubba/domain.com to the domain dir you want to mess around in.
If it's a linkingcode you're about to change, you need to escape (put an \ in front of it) certain characters: ? & /
Create a test dir with couple of test files in it to test on first.
btw, I do NOT give ANY guarantees
