Its better to read
http://www.offtopicproductions.com/tacks/3ds2de/ImportingModels.html to fully understand the whole process but here the basics
Preparations
AngrealHeal.3ds is an example name.
Models must be made up of a single 3D Studio object, which lives within the 256x256x256 coordinate space centered on the origin. (Setting the grid extents to –128..128 and turning on the grid is helpful here.) The model itself should be centered on the origin (0,0,0) because of how Unreal specifies the collision cylinders used to determine when objects are touching.
There is a limit of 9 textures on a single model, they should be square and multitude of 2 (128, 256 etc)
Limit is 512, you can use bigger textures, but they will be compressed to 512 (its a problem if you want to mask your texture)
Before saving model in 3ds format you should mirror it from left to right.
The conversion tool will only convert objects with sequence numbers in their names (Obj01, Obj02, ...). The object name itself is meaningless; it’s the sequence numbers that count. They must begin at 01 (even if that’s the only frame!) and you can’t have any “holes” in the sequence. (Under 3D Studio 4, it was easiest to use the “Snapshot” option; I’m not sure how 3DS MAX handles this.)
You’ll need a copy of the 3ds2de.exe conversion program, plus some way (Photoshop, Debabylizer, etc.) of converting files to PCX format.
http://www.offtopicproductions.com/tacks/3ds2de/3ds2de.zip
The conversion program expects an Deus Ex-like directory structure to exist before it will run. Specifically, you need:
1. a main Deus Ex directory (mine is c:\DeusEx), below which is a
2. project-specific directory (for example, c:\DeusEx\MyPackage), below which are
3. two directories, Models and Classes (e.g. c:\DeusEx\MyPackage\Models and c:\DeusEx\MyPackage\Classes)
This directory tree is what Deus Ex itself expects, so it may already be set up. If it isn’t, you’ll have to make it yourself before doing any conversions.
Converting
Place AngrealHeal.3ds and 3ds2de.exe in \MyPackage\
Create 3ds2de shortcut.
Open shortcut properties and after at the end of Target property add AngrealHeal.3ds
Doubleclick.
If everything went well, AngrealHeal files appeared in models and script folders. If not, there was a mistake so doublecheck everything. If you cant find error then read proper instructions and do it through console, so you can read error message.
Textures
First, you need 8-bit PCX versions of all of the textures that you used in the model – use Photoshop, etc.
You then need to examine the .uc file in a text editor that can handle straight ASCII text – Notepad is fine. Look for the lines that begin with #exec TEXTURE IMPORT and note that each such line ends with a material name after a pair of slashes:
#exec TEXTURE IMPORT NAME=JSpider1 FILE=MODELS\Spider1.PCX GROUP=Skins // SpiderSkin
Notice the reference to a Spider1.PCX file. Both Deus Ex and MeshViewer will need this file to properly display your model. It corresponds to whatever file you used in the given material, SpiderSkin. You need to have this file name match the name of the material’s 8-bit PCX file, renaming your PCX file to correspond with the name in the .uc file.
Using the above example, say that the SpiderSkin material was made with a SpiderSkin.TGA texture map. You’d convert that TGA file to and 8-bit SpiderSkin.PCX file. You could then either rename that file to Spider1.PCX (because that’s what the script is expecting)*
*You can also change names in script file, but that method is much more error-prone.
Make a package!
http://www.offtopicproductions.com/tacks/HowToAddCustomPackages.html