Some excellent programs listed.

The GREP port to Windows (cmd line) I find indispensable for searching within files. Win XP search is miserable for searching within files, and text editor searches have variable results.

GREP is very fast, small (100kB standalone) and convenient for searching directories on the command line.

Options can be a little weird, but the following is a start:
GREP -dn stringToFind dirName > outputFile.txt