For what ever reason, if fullbright is not used with the Intel macs, everything except for NPC/PCs is black. That part of the terrain in BD is like that even with fullbright on, it's not part of the lighting but that part of the map doesn't load properly. That black terrain has been is BD since the area was put in with 017 build, atleast for a G5 and an Intel.
Try turning on the graphics compression, I didn't have any problems with my old G5 with it on and it made things a little bit better, just follow the steps to turning it off in one of the stickies and turn it on instead. The default now is off. and I didn't use fullbright withthe G5 either, just relit the DR area. Good luck.