First you would have to get the model from Turbosquid (contact them for that).
Then you have to open and texture the model in a modeling program that supports the format that the model came in.
Then you have to export it to ".x" so your modling program must support that function as well.
After the model has been exported to ".x" you have to build an FPE file to go with it (I recomend the FPSC Entity Maker).
Once the the model, FPE and texture are all in there proper place then it should work.
There is a ton of information on this here in the forums, including some tutorials. You will have to look around to find them. I recomend using the search function to find information you want.
Some can be found here, it is one of the top threads the "FPSC Models and Media" section (I used the search function to find it):
http://forum.thegamecreators.com/?m=forum_view&t=95490&b=24
The thread is locked so you cant post anything but you can read all the info that is already there.
The person that now knows the most started with many questions. Patients and tolorance are the keys to the passage of knowledge. FPSC is Getting better. Now if we can just keep the ball rolling.