What you need to do:
There have ''V1'' and ''V2'' files,
Inside there have ''army.dff'' and ''army.txd'', you need to replace the ''army.dff'' and ''army.txd''in gta3.img,
You just need to choose V1 or V2 is better, and using IMG Tool to find ''army.dff'' and ''army.txd''.
Right click the ''army.dff'' and ''army.txd'' , choose ''Replace'', and choose the ''army.dff'' and ''army.txd'' located in ''V1'' or ''V2'' folder. Then the original army will be changed into the style in your downloaded style.
If you want to replace another ped model, just correct the ''army'' of the .dff and .txd into any other ped name.
You can find theese ped names in peds.ide.
P.s This file can't use into CJ ( player ) , it just can be use in peds models. If you really want to use this model, download the skin changer and you can play it.
Hope this can help you