As mentioned in my previous post below, the AS2 Restart should not be too complex since the specification http://www.ietf.org/id/draft-harding-as2-restart-00.txt is only 7 pages long ;-)
Indeed, the checkpoint/restart mechanism is not too difficult to implement. I have create a little VBScript prototype within my BabelAS2 open source project, you can find it at http://code.google.com/p/babelas2/source/detail?r=13.
Do not hesitate to send any questions/feedback/comments to firstname.lastname@example.org.
For now, I still need to package my Receive.asp script within BabelAS2 version 0.03. I have to explain how to configure IIS :-/ But then, within BabelAS2 version 0.04, I should be able to deliver the probably first implementation of AS2 Restart as sepicifed within http://www.ietf.org/id/draft-harding-as2-restart-00.txt!