Currently, (Visual Studio 2008 beta 2), there are some issues with trying to work with LINQ 2 SQL entities in a disconnected way and then trying to attach them.  You can generate error and if not, you will have no method of tracking the changes that occured to your entity while it was disconnected.

This is a possilbe way to handle these issues with a method of keeping Original data within the entity for use later when attaching it again:

http://www.rockymoore.com/TheCoder/archive/2007/11/03/LINQ_Disconnected_Attach_no_Change_tracking_fix.aspx