What's with all the assumptions that they are all backwards, untrained, barbarians.
Hizbollah is a very well trained, well equipped, and modern force. No, they are not up to the standards of the IDF or U.S. military, but they are giving the Lebanese a run for their money (and if it goes to full-scale civil war they will probably win).
Just because they are terrorists doesn't mean they are cave dwellers.
Oh, as for where they got the guns, probably a combination of things. The Palestinians were given a lot of M16s by both the U.S. and Israeli governments as part of the "peace process" and Hamas took over Gaza (Hamas and Hizbollah are friendly). The Lebanese forces are backed by the U.S., they have large stocks of U.S. arms. Many were probably taken from Lebanese armories, sometimes turned over by sympathizing Lebanese soldiers and police.