Chad Wanless sold his ObjectDCL to DuctiSoft some months ago.
You can find the latest version, release 3.5, on http://www.ductisoft.com.
It works for R16 and R17 (AutoCAD 2004-AutoCAD 2008).
There is also an alternative that is in Development Status : 3 - Alpha
OpenDCL is the new open source version of ObjectDCL for AutoCAD. OpenDCL is for AutoLISP programmers who want to replace AutoCAD's limited DCL (Dialog Control Language) user interface language with a rich set of modern Windows user interface elements.