1. install xcomutil into your x-com game folder (you can download it from http://xcomutil.scotttjones.com/).
2. do a backup copy of your saved game in case something goes wrong (never happened to me, but better safe than sorry) - copy the game_x (x = saved game number) folder to somewhere safe (and which u remember later).
3. open up a command prompt on x-com's folder:
- go to Start > Programs > Acessories > MS-DOS/Command Prompt
- type cd.. and press enter until you're back in the root folder ( usually C:\> )
- type cd games\ufo and press enter (replace the games\ufo bit by your x-com game's folder path)
If your xcom folder is on a different drive than c: you'll have to type the driveletter it is on followed by ':', for example d: and press
4. type xcomutil game_x vis wrt (game_x being the target saved game folder) and press enter. if all works fine you should get some results similiar to the ones in the attached image. if all doesn't work right, put your backup game back in the x-com folder.
5. load your game in x-com. the map will now be fully visible so you can easily find the last alien (for big maps it's easier to look in the minimap for alien "blips"). as soon as you end your turn any aliens not spotted by any unit will disappear again, so memorize the position of remaining aliens (or just do step 4 again). the map will remain fully explored.
note by j'ordos: in case you're not too keen on ms-dos

use windows explorer to find the xcom folder and rightclick xcomutil. There appears a menu, select 'properties' and there click the 'program' tab. There you can see the full path of xcomutil (for example : c:\games\ufo\xcomutil.exe). Now you add 'game_x vis wrt' to that line and press ok. Then run xcomutil and continue on step 5.
note2 by j'ordos : in case all of this was too confusing for you, get Martin Ptacek's XCOMSHEL (XCOMSH15.ZIP) and xcomutil (both on the xcomutil page. XCOMSHELL is a frontend for xcomutil allowing you to easily activate many of it's features (like seeing the entire map)
note3 by supsuper: a fast way of overcoming step3 (if you have windows xp) is to install the Open Command Window Here powertoy. that way all you have to do is right-click x-com's folder and select Open Command Window Here from the popup menu.
any questions just ask, specially if you didn't understand what i said

Edited by SupSuper, 19 October 2003 - 12:54 PM.