Develop Office Client Applications using Visual Studio
When you debug a SharePoint workflow project, the workflow deployment process copies the feature.xml and workflow.xml to a feature directory on SharePoint. You can configure your solution to deploy other files as well. For example, you might want to deploy InfoPath (*.xsn) files that provide a UI for the workflow, or a file that contains localized resource strings.
To do this, open the feature.xml file of your solution, and add an element named ElementFile for each file that you want to deploy along with your project. Set the Location attribute of the element to the name of the file.
Note If the file is located outside of the root directory of the SharePoint solution, ensure that the name includes a relative path.
The following example specifies an InfoPath form named InitiationForm. This form is located in the root directory of the SharePoint solution so the name does not require a relative file path.
Description="My SharePoint Workflow Feature"
<ElementManifest Location="workflow.xml" />
<ElementFile Location="InitiationForm.xsn" />
<Property Key="GloballyAvailable" Value="true" />
<Property Key="RegisterForms" Value="*.xsn" />
The VSTO documentation has been updated with this information and will appear on MSDN soon.
Interesting point at blogs.msdn.com
More on InfoPath forms deployment for SharePoint workflows at http://blogs.msdn.com/nikhil/archive/2008/01/22/infopath-forms-deployment-sharepoint-workflow-in-vs-2008.aspx.