yes, use either an manual installer eg IMG EDITOR 2.0 or an automatic one, both gets the job done. with the manual one you're going to navigate to GTA SA directory \models and open gta3.img. to locate the weapons search nitestick, this will get you to the weapons section. if the weapon you're modding is M4, you find m4.dff and m4.txd and replace both with the two files you got in the mod folder. click rebuild archive. now you can close it and open game