Can't find the thread now, but I sent the form letter to iNav's support group asking then to release a SDK. I got some of the usual response, but they hinted at better things to come:
Hi Jeff:
Unfortunately, we have put SDK development project on hold due to lack of engineering resources.
However, we are modifying the user interface and hopefully will have that available w/ release of v2.2 in May 2006.
Thank you and we apologize for the inconvenience.
Support Team
www.inavcorp.com
Hopefully it's tailored for a pc touch screen and not a PPC.