the process your looking for is referred to :
texture mapping
or
uv mapping
or
uv texture mapping
LAYMANS
think of a cereal box without the contents.
pull apart the glue and look at each face of the carton as if its two polygons creating a square or rectangle for each side, see which direction the texture has been painted on the box to achieve the desired result. this definition is at its simplest form.
once you have your map it aligns itself with every polygon on your model.
then with a 2d package you can paint the graphics into the correct spot.
the x file format retains this information when you export the file and keep the texture with it.
check out your package for a uv mapper tutorial or look for a tool that plugs into your current 3d package.
check out wiki for a definition
http://en.wikipedia.org/wiki/UV_mapping
or look at it visually
imagine this is the map for a zombie created by psionic for his tutorial
and the link
http://www.psionic.pwp.blueyonder.co.uk/tutorials/lowpoly/zuvm.html
Personally I cannot live without this $50 US package
http://www.unwrap3d.com/
features
Easy to use UV mapping editor.
Fully OpenGL rendered viewports, with multiple layouts.
Standard planar, box, cylindrical, and spherical UV mapping.
Unfold UVs for unfolding faces into a 2D pattern.
Pelt mapping for unwrapping organic models.
Conformal mapping for preserving face angles.
Stretch UVs for spreading out overlapping faces.
Relax UVs to help minimize texture distortion.
Pack UVs onto one texture to improve cache performance.
Untangle UVs to separate overlapping UV coordinates.
Interactive camera, planar, cylindrical, and spherical UV mapping.
2D editing tools include moving, scaling, rotating, flipping,
mirroring, straightening, stitching, and welding of UVs.
3D editing tools include triangulating, untriangulating,
flipping, welding, unwelding of vertices and faces.
Copy/Paste UVs when working with mirrored geometry.
Material editor for editing material and texture properties.
UV maps get updated in real-time.
Export UV maps as Photoshop vector layers.
Export UV maps to high resolution bitmaps.
Pan and zoom in UV mapping space.
Import/export multiple UV sets.
Paint in 3D using vertex colors.
Fast lasso and rectangle selection tools.
Select by vertex, face, group, or material.
Customizable hotkey shortcuts.
Auto update of textures from file.
Auto detection of texture aspect ratio.
99 level undo system by number or storage.
Soft selection for editing subdivision surfaces.
Subdivide UV coordinates and geometry.
Plugins that allow unlimited 3D import/export functionality.
Import textures in variety of 2D graphics formats.
Create plane, box, cone, cylinder, sphere, geosphere,
pyramid, prism, tube, torus, capsule and text primitives.
Runs under Windows 95/98/ME/2K/XP platforms.
it also allows me to convert many game models
Game Formats
Description Extension Import Export
Alias Wavefront OBJ yes yes
3D Studio 3DS yes yes
3D Studio ASCII ASC yes yes
3D Studio Max ASCII ASE yes
AutoCAD DXF yes yes
Truespace COB yes yes
Autodesk FBX FBX yes yes
Lightwave LWO yes yes
Microsoft DirectX X yes yes
SoftImage|XSI XSI yes yes
AC3D AC yes yes
Anim8or AN8 yes
Cartography Shop CSM yes yes
3D GameStudio MDL yes yes
Nichimen Nendo NDO yes
Blitz3D B3D yes yes
DarkBASIC DBO yes yes
Genesis3D ACT, BDY yes
MilkShape3D MS3D yes yes
Metasequoia MQO yes yes
Torque Game Engine DTS yes yes
Ogre 3D Engine XML yes yes
POV-Ray RAW RAW yes yes
POV-Ray POV POV yes
OpenGL CPP CPP yes
Apple Quickdraw 3D 3DMF yes
Adobe Illustrator AI yes
BioVision Hierarchy BVH yes
Hollywood FX HFO yes
Stereo Lithography STL yes yes
Object File Format OFF yes yes
RenderMan RIB RIB yes
VRML 1.0, 2.0 WRL yes
Battlefield 1942 SM, RS yes yes
Black & White L3D yes
Command & Conquer: Renegade W3D yes
Descent 3 OOF yes
Delta Force 5: Black Hawk Down
Delta Force 4: Task Force Dagger
Delta Force 3: Land Warrior
Delta Force 2
Delta Force
3DI yes
FarCry POF yes
Freespace 1/2 POF yes
Half-Life: Opposing Force MDL yes
Half-Life: Opposing Force SMD yes yes
Homeworld PEO, GEO yes
Neverwinter Nights MDL yes yes
Quake 1 MDL yes
Quake 2 MD2 yes
Quake 3 Arena MD3 yes yes
Return to Castle Wolfenstein MDC yes
Kingpin: Life of Crime MDX yes
Quake 1/2/3, Half-Life BSP yes
Doom 3 MD5MESH,MD5ANIM yes yes
Heavy Metal: FAKK2
Medal of Honor: Allied Assault
Medal of Honor: Allied Assault Spearhead
Medal of Honor: Allied Assault Breakthrough
SKB,SKD yes
Shogo: Mobile Armor Division
Blood 2: The Chosen
Aliens vs. Predator 2
The Operative: No One Lives Forever
Global Operations ABC yes
Lula 3D
Psychotoxic V3O, VMO yes
MotorRacer 3 F3D yes
4x4 Evolution SMF yes
Rainbow Six Rogue Spear QOB, ROB yes
Rome: Total War CAS yes yes
Call of Duty 1/2 XMODEL yes yes
SWAT 3: Close Quarters Battle GSM yes
Tread Marks LUV yes yes
Re-Volt PRM yes yes
Serious Sam MDL yes
Birth of the Federation HOB yes
Star Fleet Command 1/2 MOD yes
Star Trek Armada 1/2 SOD yes yes
Star Trek: Voyager - Elite Force MDR yes
Jedi Knight: Dark Forces 2 3DO yes
Jedi Knight 2: Jedi Outcast GLM yes
Star Wars: Empire At War ALO yes
Star Wars Galaxies MSH, MGN yes
The Sims SKN, BMF yes yes
Unreal Tournament 3D 3D yes yes
Unreal Tournament PSK/PSA PSK, PSA yes
Vampire: The Masquerade - Redemption NOD yes
Warcraft 3: Reign of Chaos MDX yes
World of Warcraft M2, WMO yes
Worldcraft MAP, RMF yes
2D Graphics File Formats
Description Extension
Windows Bitmap BMP
Truevision Targa TGA
Joint Photographic Experts Group JPG
Portable Network Graphics PNG
Zsoft Paintbrush PCX
Adobe Photoshop PSD
Microsoft DirectDrawSurface DDS
Portable Pixel Format PPM
Portable Grayscale Format PGM
Portable Bitmap Format PBM
Serious Sam TEX
Descent 3 OGF
Homeworld LIF
Jedi Knight: Dark Forces 2 MAT
Rainbow Six Rogue Spear RSB
LithTech Shogo/Blood2/AvP2/NOLF/GOps DTX
Warcraft 3/World of Warcraft
BLP