@rundocuri- I don't recommend using a regular nail gun for installing materials like wall trim pieces. A nail gun is very powerful, and could easily damage trim materials because they are thin and delicate compared to the type of thick wood used for building. This is why finish nailers were created.
On the positive side, you can most likely find a finish nailer for an affordable price. Try shopping for one at your favorite home improvement store during a sale, or look for a used one at pawn shops in your area. Just make sure that you have it tested first before buying a second-hand finish nailer.
If you have your heart set on finishing your wall trim project without buying additional equipment, you could just resort to using a hammer to put your trim pieces in place. Since wall trim is made of thin wood or faux wood, it is actually quite easy to use a hammer and trim nails to install it.