There is a members-only topic in the Uplink Forums called "Development". This topic is intended for Introversion developers and owners of the Developer CD only.
If you don't have access, you need to send an email to email@example.com. In that email you need to tell us your Forum username, and your introversion transaction ID. You need to have already registered your username as a standard forum user of course. You will have received your introversion transaction ID by email when you placed your online order for the Developer CD. We need that number to make sure you did actually order the CD from us ;)
We will then give your Forum username access to the Developers forum.