So i just picked up BG from on here last night, so far i'm really into it, but i have a nagging question thats been bothering, why does my character's AC keep going down when i equip better armor?

Now i know it's been a good while since i played a D&D game, but as far as i know, the higher the better.

What gives?

Lower is better in earlier versions of D&D rules.

They changed this around the time Neverwinter Nights was made, I think, since from then on it's been higher is better.

Both BG and BG2 use 2nd edition rules but BG2 included a few bits of 3rd. Both games use the AC system of 2nd edition where a low armor rating is good.