Get a picture of your truck on the web and then right click it and click properties. Then highlight the properties part and go to your signature here and paste it. After that you can preview it to make changes. I just did mine yesterday thanks to fade2black.
There are many ways but I used snapfish. Google snapfish and sign up for free. Then you just upload the pictures you want to use and then take the properties of off your snapfish held picture and then put it on your sig. Try it and let me know if you have any problems.
As far as hosting goes I have had very good experiances with imageshack. Most people do, until they clear cookies and cant figure out how to log back in.
I'm trying them as we speak. But how do you resize them to 125x125 for your avatar? I can get my pictures there but I'm not sure how to resize them there.
I resize with paint, my wife resizes (and more accuratley so) with code. Im dumb when it comes to code but it shouldn't be too hard to figure out. size=125 or something along those lines.