Yes, the Digital AV Adapter announced with the iPad 2 will work with the original iPad. However, not all features of the adapter will operate with the original iPad.
Video mirroring will only function with the iPad 2, and the iPad 2 will support up to 1080p resolution HD video. The original iPad will only output 720p HD video using the Digital AV Adapter.
On both the original iPad and iPad 2 the adapter delivers digital audio via HDMI cable to a compatible television. Both devices can be charged if the Digital AV Adapter is connected to a USB port or charger with a 30-pin dock connector.