I was googling and I found some 3d models of some game characters!I was wondering if I could use the 3d models to create meshes of hair,weapons and clothes?And if it's really possible how can I do it?

Yes it is, but that's a tad complicated. I believe i said to you earlier that Rigging is the big issue (Frankensteining only works when you chop off sim parts, not foreign meshes). You would have to scale the meshes to fit the sims, making extra sure that the hands especially are perfectly in synch with sim hands; then, rig the model FROM SCRATCH and adjust the UV to work with the sims. Accessories would be much easier to fit but are harder to "link" (if you read any of those tutorials then you'd understand.)

BUT!!! You cannot claim any credit for these or upload them to the site. MTS is very strict about that...

Oh!So I have to stick to creating on my own and Frankensteining etc!Ok thanks once again Ken!