Lies, lies.... all lies....
According to this page
http://www.adobe.com/products/photoshop/cameraraw.html your camera is only supported in the CS2 version of Camera Raw.
Also, according to this page
http://www.adobe.com/products/dng/main.html it says DNG is only supported in CS2.
Both of these pages appear to be incorrect
You need to download the Camera Raw update for PS CS. The Nikon D70 was supported as of Camera Raw 2.2 for Photoshop CS. There's also DNG converters for download once you're at the update page. The latest version of Camera Raw for CS is 2.4. Camera Raw 3 is only for CS 2 (that's why it's listed under the CS 2 section of the Photoshop Downloads Page)
Head over to the
downloads page at Adobe to pick up the updates.
If you want, there are plenty of other programs that will work with your D70 other than Photoshop and the Nikon software if you're interested.
Capture One Pro and LE
Bibble
VueScan
are three that come to mind right away.