A SIMPLE search and replace for multiple files sample:
http://www.gabeanderson.com/life/archives/000392.php
This is in Linux, done with bash (I think).
And I quote:
for fl in *.php; do
mv $fl $fl.old
sed \'s/FINDSTRING/REPLACESTRING/g\' $fl.old > $fl
# rm -f $fl.old
# when uncommented, the above line erases original file.
done