Go to your Fallout directory, for Win7 with Steam it'll be Program Files (x86) - Steam - steamapps - common - fallout
Open up the file "ddraw" with notepad
Highlight everything and then copy/paste the following:
Spoiler [Main]
;Change to 1 if you want to use command line args to tell sfall to use another ini file.
UseCommandLine=0
;XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
[Speed]
;Set to 0 to disable everything in this section
Enable=1
;The speeds corrisponding to each slot in percent. (i.e. 100 is normal speed)
SpeedMulti0=50
SpeedMulti1=100
SpeedMulti2=150
SpeedMulti3=200
SpeedMulti4=300
SpeedMulti5=500
SpeedMulti6=1000
SpeedMulti7=100
SpeedMulti8=100
SpeedMulti9=100
;The initial speed at game startup
SpeedMultiInitial=100
;XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
[Graphics]
;Set to 0 for 8 bit fullscreen
;Set to 1 for 8 bit windowed
;Set to 4 for dx9 fullscreen
;Set to 5 for dx9 windowed
;Mode 1 requires your desktop colour depth to be set to 32 bit
;Windowed modes incur a performance hit. (Modes 1 and 5 more so than mode 3)
;The 16 bit colour modes cause movies to display incorrect colours, and slows down fades
;dx9 modes cause some corruption of movies, but not as bad as 16 bit colour modes
;dx9 modes work with fallout 1, but results in movies being completely corrupted
Mode=4
;Refresh the screen every x frames. Set to 0 to disable frameskipping.
;If you don't want frameskipping on initially, but may want to enable it later, set this to 1
;This has no effect in fullscreen mode or in dx9 modes
FrameSkip=0
;If using a dx9 mode, this changes the resolution
;The graphics are simply stretched to fit the new window
; this does _not_ let you see more of the map
;If you want to use an upscaling filter other than the hardcoded once listed below, place a dx9 effect file called 'global.fx' in data\shaders
GraphicsWidth=1920
GraphicsHeight=1080
;If using a dx9 mode, this changes the settings of the global shader
;Set to 0 to disable, 1 to use only if screen res > 640x480, 2 to use if screen res != 640x480 or 3 to use always
GlobalShaderMode=1
;Set to something other than 0 to apply a software scaler in graphics modes 4 or 5
;0 - without scale filters
;1 - 2xSai
;2 - SuperEagle
;3 - Super2xSai
;4 - hq2x
;5 - AdvancedMame2x
ScaleFilter=0
;Set to 1 for a linear texture filter, or 0 to disable
TextureFilter=0
;XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
[Input]
;Set to 0 to disable everything in this section
;This will also disable any input related script extender functions and the keyboard commands used to control other sections!
Enable=1
;Set to 1 to enable the mouse scroll wheel to scroll through your inventory
UseScrollWheel=1
;The mouse Z position is dividied by this modifier to calculate the number of inventory
;slots to scroll. My mouse moves 120 pixel in the z direction for one click of the mouse
;wheel, but this may vary depending on your mouse manufacturer and windows settings.
;Set to 0 to only ever scroll 1 click
ScrollMod=0
;Adjusts mouse sensitivity to some percentage of normal.
;Negative values are valid, if you want your mouse axis reversed for some reason
MouseSensitivity=80
;DX scancode of a key to press when the middle mouse button is clicked
;The default of 0x30 toggles between your two weapons
;Set to 0 to disable
MiddleMouse=0x30
;Set these to 1 if you want fallout to access the keyboard or mouse in background mode
BackgroundKeyboard=0
BackgroundMouse=0
;XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
;The modifier key you have to hold down to change any speed settings
;If set to 0 if you don't want to use a modifier key, or a DX scancode otherwise
;Set to -1 for either ctrl key, -2 for either alt key or -3 for either shift key
SpeedModKey=-1
;A key to press to toggle the speed tweak on or off
;Specify 0 if you don't want a toggle key, or a DX scancode otherwise
SpeedToggleKey=0x00
;The keys corrisponding to the 10 speed slots
;Set to 0 to disable a slot, otherwise specify the DX scancode of the key you want to use
SpeedKey0=0x52
SpeedKey1=0x4f
SpeedKey2=0x50
SpeedKey3=0x51
SpeedKey4=0x4b
SpeedKey5=0x4c
SpeedKey6=0x4d
SpeedKey7=0x00
SpeedKey8=0x00
SpeedKey9=0x00
;The modifier key you have to hold down to change any graphics settings
;Set to 0 if you don't want to use a modifier key, or a DX scancode otherwise
;Set to -1 for either ctrl key, -2 for either alt key or -3 for either shift key
GraphicsModKey=0
;Increase/decrease frame skip.
IncreaseFrameSkip=0x51
DecreaseFrameSkip=0x4f
;Toggle the global shader on or off
ToggleGlobalShader=0x52
;Changes the current scaleing and texture filters
CycleScaleFilter=0x53
ToggleScaleFilter=0x4f
ToggleTextureFilter=0x50
;End
Adjust "GraphicsWidth=1920" and "GraphicsHeight=1080" to whatever resolution you want. Your native resolution may be best, but some resolutions will cause a bit of stretching. My 1920 by 1080 monitor using that resolution does stretch slightly, but it isn't really noticeable.
As for Fallout 2, I'm pretty sure you can paste the same thing in the FO2 folder with the same file. However, I do recommend the Fallout 2 Restoration Project (google it, shouldn't be hard to find), which adds a bunch of good content and fixes bugs. It also has resolution options in the options menu as well as an option that fixes rainbow-ness, but I don't remember which. Just mess around with it until it works.