Welcome to "How to PMI Tutorial!" In this tutorial, you will be adding a Long Sword into Bloodgulch! This tutorial is recommended for Expert and very good modders only! This will be very hard for beginners.
First off make a folder named "Project" or something, then in it make 3 subfolders "Bloodgulch Extract" "Bloodgulch BSP" "NEW ITEMS", or at least 3 folders.
To add folders Right click in the folder and go to  NEW -> FOLDER
Be sure you copy and paste a BRAND NEW, bloodgulch.map into the Sub Folder, BLOODGULCH EXTRACT. If you need a new bloodgulch.map and don't have a normal download a tutorial from my web site.
Now let's go ahead and open up Halo Map Tools V3.5, and go to File -> Open  or just click the open map file button.
Open up bloodgulch.map located in your BLOODGULCH EXTRACT Folder.
Then with Bloodgulch.map open in HMT V3.5, go to  TOOLS -> EXTRACT ->BATCH EXTRACT.
 
Click the checkbox "Extract Metadata" , then click "Browse" and browse to Project/BLOODGULCH EXTRACT and hit "OK".
Then press the "Start Batch Extraction" Button, then it will ask "Extract BSP?" Yes, always choose yes when PMI'ing.
At the end of the batch, it will seem to "FREEZE", don't worry, it's extracting the map's BSP, that's the biggest part!
Now go to TOOLS -> EXTRACT -> BSP/MODEL Sections.
Then extract it to Project/BLOODGULCH BSP.  Make sure you have bloodgulch.map open in HMT though!
Then when it's done it says, "Files saved".
Now in HMT, go back to FILE -> OPEN.
Choose yes...
Now go find a10.map,  It should be somewhere in  C:/Program Files/Microsoft Games/Halo/Maps, but I just copied it to Project/New Items.
Go to the Tag:  [scen] Scenery (33 items), then go down to.....
Click "vehicles\fighterbomber\fighterbomber_scenery and go to the top click the checkbox "recursive" and hit the "Save Meta" Button.
Save it to NEW ITEMS..
Then it will say "FINISHED EXTRACTING"
Then while a10.map (PILLAR OF AUTUM) is open, go to Tools -> Generate Raw Model Offset List (CVS File).
 
Save it anywhere...
Ok it's saved!
Now go to:  Tools -> Extract -> Raw Model.
Now when that loads, click the button, "LOAD CVS FILE" , and when the browse box comes up it should show, "offsets.cvs, or offsets". click it and hit "OPEN".
Find the thing you extracted, in this case its "vehicles\fighterbomber\fighterbomber and click "EXTRACT".
Save it to: Project/New Items/vehicles/fighterbomber/.
Then it says "DONE!".
Now go to: Tools -> Model DeCrapper/BSP Builder.
For the Existing Vertex Area is in: Project\BLOODGULCH BSP
For the Existing Index  Area is in: Project\BLODGULCH BSP
For the Existing BSP Block is in: Project\BLOODGULCH BSP
Here..
They show up with no other files, easy!
Ok now that those are filled in let's add the Longsword to the List, to do Right click in the box and click "ADD".
If it says: Now Raw Vertices File Found, you need to go back to the CVS File stuff. Click Fighterbomber.mod2.meta, and click "OPEN"
Ok time to hit "De-Crap These Models and Build a New BSP Chunk While We're At It"
Now this is done.
Now browse to PROJECT/BLOODGULCH BSP, and right click the file "bloodgulch.sbsp.meta", this is the file that we just made, it's the new BSP CHUNK, copy it.
Now browse to "PROJECT/BLODGULCH EXTRACT/LEVELS/TEST/BLOODGULCH, and in the folder right click and hit "PASTE".
Over rite =YES
Now copy the entire contents of the NEW ITEMS folder. Expect for like the map or offsets.
And go to PROJECT/BLOODGULCH EXTRACT, then right click and hit "PASTE".
Over rite any files.
Now it's time to build the map! So go to Toos -> Rebuild Map
For the Original Map, go to Project/Bloodgulch Extract/Bloodgulch.map
Choose yes..
Now click the button [ADD], and go to Project/New Items/Vehicles/Fighterbomber and select all the files (not in bitmaps or shaders or the other folders) Then click OPEN.
 
Now it's time to click "Build"
Click YES.
Browse to: Project/Bloodgulch BSP/bloodgulch.vertices.new.
When it ask Have any new indices added to the oringinal bsp chunk? choose yes and browse to Project/Bloodgulch BSP/indices.new.
Choose yes...
Then wait for it to finish...
Ok we are done.
Now since we used scenery we don't have to go into HMT and change stuff. So open up Sparkedit V3.02, and open up the bloodgulch.map.rebuild.map located in Project/Bloodgulch Extract/bloodgulch.map.rebuild.map.
Now when it loads, go to Tools -> Import Tag Into Scenario
The Object Tag Type: choose scenery   
Then unregistered tags choose Vehicles\fighterbomber\fighterbomber_scnerey.
Put it in and go to File -> Save Changes
Open up halo.. And here's a picture..
  Enjoy!
Downloaded this tutorial from Here
Tutorial by: BryanJK