Absolutely!  You'll need a 3d modeling program to do it, though.  I use 3ds Max, but that can get rather expensive.  There's a link floating around here somewhere that leads you to the Softimage/XSI mod tool.  Personally, I find XSI rather complicated, but I know for a fact that someone has created a thread with multiple tutorials for modeling in the program.  There are also other free 3d modeling program, though I'm not sure which they are (some other helpful person will pop in and tell you, I'm sure). 

As a side note, the Forge Tools don't actually have anything to do with modeling.  There's a map editor, a particle editor, some conversion tools, and some reference files.  The two editors are still very usable, but if you're looking for conversion tools or reference files, there is a forum member named Harpo99999 that has created a suite of files for conversion and has also uploaded all current reference files (which I think is on page 2 of this modding forum).