In order not to be mistaken with a choice, right-click on desktop, choose "Properties" for Windows XP or "Permission " screen for Windows 7. View the set value and remember it.
Start the game and go to menu "Options" -> "Video". There you will find option "Resolution screen". It can change only to download new games (i.e. from the main menu). In addition, the number of permits is strictly limited and extreme options are not provided.
If the switching resolution in-game leads to errors and freezes –use the launcher. In the game folder there are two exe files: the first runs of the game in full screen mode, the second small window presets. In this you should choose "video settings" and change the resolution. Ultra-high options in this menu have not been fixed.
Navigate to the folder "My documents" of the user who installed the game. Next, go to My Games / Fallout 3. Inside you will find the falloutprefs file.ini, which should open with any text editor (e.g. Notepad). If you are worried that may damage the contents of the file, create a backup, highlight it and alternately pressing Ctrl + C and Ctrl + V. you can then remove the faulty file and rename the created.
Enable the option "Search" and using it find the combination of iSize W. You will discover a couple of options: iSizeW=# iSizeH=#. Instead of the first "grid" enter the width value in pixels (greater), and the second is the height (lower). The advantage of this method is that you can specify any value, including ultra-high. However, experimenting with unusual combinations is not necessary.