Hi Dave.
In 2007 you can make data connections off-line but I am not sure this is possible with the default Access connections. If you were using SQL Express and web services that could work.
Probably the best would be to have two form versions.
One online, which I think you already have.
One that is similar in Schema but is for off-line.
Then setup on-line form to connect to saved XML from off-line form and import it and then submit.
So the on-line form will have an XML data source and consume the saved documents from off-line and inject the data in you data fields and then submit it.
There are some other methods but that is probably the simplest.