The benefits of fully trusted InfoPath forms

You can create fully trusted InfoPath forms which have a higher privilege level than the default.  There are some simple steps to follow when you need to go down this path and they are all well explained within this document:

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/ipsdk/html/ipsdkUnderstandingFullyTrustedForms.asp

The important things to take away from that article are that fully trusted forms are A) Urn based as opposed to Url based, B) The xDocument attribute can be modified to include the "requireFullTrust" attribute setting and C) these types of forms are "Registered" on the target PC.

As also mentioned within the article, if you are heading down this path then you really must look into using the RegForm command-line utility to simplify the package and deployment process into a no-brainer.  RegForm has some neat options for making and packaging trusted InfoPath forms.  This tool makes it simple to package Urn based forms in an .msi to facilitate simple installation on a users computer.

One of the benefits of urn based, custom installed forms is that you can target Xml documents to be opened with that form template by including the urn in a processing instruction within your Xml document.