Getting a ship model in the game:
Pre-step) Make sure your model doesn't have intersecting polygons and has less than 2000 polygons. Intersecting polygons will look bad in-game, and exceeding the polygon limit can cause FS2 to crash.
1) You'll have to convert the ship to a POF using POFCS
2) Move the ship model to Freespace2\data\models
3) Convert any textures to 256-color PCX files and move then to Freepace2\data\maps
4) Using
VPView, Open root_fs2.vp and extract ships.tbl (it'll be in "tables") to Freespace2\data\tables.
5) Open ships.tbl with an editor like Notepad.
6) In ships.tbl, copy the entry for the GTF Ulysses and paste it right above the original entry. Change the name ($Name) to the name for your ship and change the model file ($POF file) to the filename of your .pof file.
7) Open up Freespace 2 and look for your ship in the tech room.
If you have problems starting Freespace, try deleting the comments (lines starting with ";") at the beginning of ships.tbl.