Sonicteam has posted some information regarding the PC release of Sonic Adventure DX Director’s Cut. The page mentions that the game can be run in 640×480 or 1280×1024 resolutions, and will consist of 2 CDs. The (Japanese) release date has been set at the 18th December 2003, the same day as Sonic Heroes.
Sonicteam has also released the specifications for the game (translation here).
Source: Sonicteam