an_idol_mind
Explorer
I ran my first 3rd edition game before either the DM's Guide or the Monster Manual came out. I remember using the orcs and hell hounds that were presented in the back of the Player's Handbook, and the rest of the foes were adventurer characters. I didn't need the DM's Guide to figure out magic items (a +1 sword or a ring of protection works the same in every edition). For experience, I determined how well the game went, and gave the PCs an appropriate award for the session (usually 30-50% of what they needed to reach a new level). As the other books were released, certain aspects got added into the setting -- a shadowdancer NPC appeared after the DM's Guide came out, and monsters like ankhegs, ettercaps, and a bodak villain were introduced after the Monster Manual hit the stands. Other than that, there wasn't any feeling of a huge transition, and the game ran smoothly even when it was just the Player's Handbook.