is this a weapon or a entity? anyways to UV map import a texture(i hope you know how to do that)and press control+T and move and scale the selected vertexes which changes where the texture goes.
now for very detailed UVmapping you have to select individual FACES and press control+T and UV map them as well.
as for animating and exporting in milkshape directly to .x is nigh impossible with either plugin
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position and size is very important to export the exact size you made it go to the JT exporter and set the position scaling option(default is .1) to 1 and you are going to have to screw around with the other options depending on how you want the model to look like.
to make lower poly select the whole model and go to tools and "Clean" removes any excess polys and otherwise no real clue as to make it low poly
I know not what WWIII will be fought but I do know that WWIV will be fought with sticks and stones-Albert Einstein