Assingning default variable to a custom content type ???

[SharePoint2010]

Hey. I have created a workflow with Sharepoint Designer 2010. But I have a problem: I have created a content type with "Custom Task Wizard" and added "multiple lines of text" form to it. I have to assign a default variable which is the "multiple lines of text" form of other custom content. I was wondering if someone can help me Thanks...