kracken is right -- here are some more detailed instructions:
1) Wait until you get the next mission. Write down the Location that comes up -- you will use this to find and modify the mission.
2) Quit the game. Using your favourite archiver, e.g. 7-zip.com, unzip 0ufos.pk3 into into the base/ subdirectory of your UFO installation directory, so you end up with base/ufos/.
3) Using your favourite text-editor, edit missions.ufo from that directory. Search for a mission whose Location matches the one you wrote down in step (1). Once you've found it, add the following line to it:
onwin "cp_uforecovery 0;"
4) Restart the game, play the mission. If you win, you should have a Scout UFO.
HTH,
nemchenk