first of all right click in your 2D area and go to misc > model
go to your xmodel folder.

If you dont have an xmodel folder you may need to extract them from your COD pak files. press enter to add your model. now if your xmodel folder isn't in your /main directory like mine i keep in my mapping section you may get this.

If you get this simply Press N and change the directory to

xmodel/yourmodel as shown below

there you go a simple tutorial on how to add models