Pleases note: This is public domain information without any guarantees.  Use at your own risk.

Start->Run->cmd
Use the "cd" command to get to the directory that you want to search, or just type "cd C:\" to search your entire C drive



echo start > findresults.txt
for /F %i in ('dir /b /s *.type') do (find /N "searchtext" %i) >> findresults.txt

The first line clears the results file.
replace .type with the type of extension you want to search through
replace searchtext with the text you want to search for
this will find all instances of the search text in all files of the provided type and write the results to findresults.txt



To Search file names:
echo start > findresults.txt
dir /s /b | find "searchtext" >> findresults.txt

replace searchtext with the text you want to search for
this will find all files in all folders at your current location and write the results to findresults.txt



warning: double quotes really complicate things, avoid them or look for documentation elsewhere