(1) Get the model in Blender 3D. Import obj or fbx (with animation) files into Blender 3D and begin making revisions. Blend files work be default and don't require any special steps to load.
(2) Make revisions. Before making revision you may see a box if you imported a obj or fbx file. Simply go to the right hand corner and delete the default cube. Next you will need to setup a material file which is a different step for CoD2 or CoD1.
For CoD2 name the material file same as material name you will be using in Asset Manager. Should be like mtl_axis_stickynade or whatever. Just don't put .001 at the end of the file.
For CoD1 make a material file and link the image to it. CoD1 doesn't have a material file system and works with jpg, dds, tga (small generally only)
(3) Save the file as a blend file or fbx (has animation). Use the blender-cod plugin to export XMODEL_EXPORT file. For weapon models make a viewmodel and worldmodel. Ex: vm_stickynade.XMODEL_EXPORT and wm_stickynade.XMODEL_EXPORT.
(4) Use Asset Manager to generate xmodel, xmodelsurfs, xmodelparts, iwi files (CoD2+) and other goodies.
You will have to create gdt file and material (CoD2) and 1-2 xmodel files (2 if weapon model). Once you have everything setup to your liking convert one thing at a time. Asset Manager will create xmodelparts and xmodelsurfs automatically if you made an xmodel.
Remember when dealing with weapon xmodels, you should save as viewmodel and make two xmodel both with different XMODEL_EXPORT names. Viewmodel and Worldmodel are the same but you need both for weapon models.
Asset Manager should be set to run as admin and XP SP3 compatibility mode (otherwise it cannot find hidden compatibility files.
(5) Closing notes. CoD2 may or may not work with multi-able material files. lets say you have shotgunwood.iwi, shotgunbarrel.iwi, shotgunshell.iwi ect. You may have to create many material files but some how make sure the images are mapped to the model correctly.