Hi again,
Sorry for the strike one. I was a bit harried when I whiffed that one.
OK, so with more thought on a Saturday, I think that it should be easy to generate this from fields. The problem is going to be creating a file that is then attached or outputted.
You might be able to use concat to build up the ics file using the fields and static text. Then, you could convert it into BASE64 and set a file attachment field to the value. qRules has DecodeBase64 but it does not have EncodeBase64, but it would be easy to add. Is qRules an option here? If so, send us email and we'll get it in the next release. Then, you could save the attachment as a file to a doclib using the qRules SaveToSharePoint command. After it's converted to a link via SaveToSharePoint, users could click on the link to add to their calendar. Codeless for you, but requires qRules.
Suppose concat doesn't work because it's hard to get the line breaks or something. Well, you could use some kind of an XSLT transform to create the ics file format. Here again, qRules transform command might just do the trick and the result could be saved to a text string.
But, how to get it out into a file without full trust. If you were using the InfoPath Filler, the only way to write it to the local file system is to use full trust. qRules has a command for writing to the local file system, but who cares? You are using the browser.
Workflow custom action could be implemented to take the XML file and generate an ICS file that was mailed to the users. That's code though, albeit not in InfoPath.
We could write a Web service to take the fields and create the ICS and return a link to it that would be clickable and open up in Outlook. Would be simple.
Oh, but it's way easier than that... check this out: http://www.youtube.com/watch?v=4mS8WrJuRQY
You can use SharePoint 2010 out of box to generate these via the owssvr method. What does this mean? It means you just need to create the calendar request. Codeless way to do that would be CAML - see the webinar we did this week. Or, you could use qRules to generate it. Then, create the URL to owssvr using concat, and have them click on that.
This would be very cool to put in a weekly webinar. Let me know if you need help doing it and we'll try to whip something up.