You can enter the Dark Forest from the start of the game, assuming you can make it to the entrance alive. After hitting the gong and entering the wastelands, you can not leave to go anywhere else (from then on it is just the wastelands and Black Ring dungeons).
The Dark Forest 'leads' to the wastelands only in the sense that it must be done first (a couple of the council member quests are mostly or completely based there).
Go do everything you want to do and explore everywhere. When you are completely finished, go borrow money from Sire Patrick <img src="/ubbthreads/images/graemlins/badsmile2.gif" alt="" /> and then hit the gong.
