Well, you can set events to have treasure be found by the players in certain locations.
As for THAC0, THAC0 stands for "To Hit Armor Class 0." In AD&D, the lower the Armor Class (AC), the better - an AC of 10 is basically a normal human's unarmored AC, while an AC of 1 would be what a fully-armored (full plate) and fully-shielded (tower shield) man would have.
As THAC0 is the number you need to roll (from 1-20) to hit AC 0, the higher the THAC0, the better. If you have a THAC0 of 20 and wish to hit someone wearing leather armor (AC 7), then you will have to roll a 13 or better (out of 20) to hit.