Do yourself a favor (unless you can pick up the tab for 3DSMax) and get Milkshape.
You can model,texture and animate a model with it.And you can do a bunch of other stuff like make models in a wide variety of formats.
Even if you don't model Milkshape is worth the money just for the files it converts.
For the price tag (less than $30 USD) it's one heck of a deal.
I used Milkshape to animate the weapons I make and I even wrote a tutorial on how to animate a weapon using Milkshape (cheap plug).
You should be able to find it in the stickies at the top of this board.
I use both WCS and Weapon Creator for importing my weapons into FPSC.
They are two very different apps that basically accomplish the same thing but I recommend them both.
As has been pointed out though the weapon must be modeled,textured and rigged separately.These programs only import your weapon into FPSC.
Of course you can import your weapons into FPSC by hand.Good luck with that.Before WCS and Weapon Creator came along that is how we had to do it and it is a very long and aggravating process.
You might search this forum for weapons since there are a glut of them available for free.Or get model packs 9 and 10 if you can afford it.Best weapons ever made IMO (no disrespect to Jon or Simon...their stuff is great but there's only one Errant AI just like there's only one Michael Jordan)...model packs 5 and 6 also have excellent weapons.
Please have mercy and use the search function.