Under normal circumstances you cannot move a workflow designed in SharePoint Designer to another site, or into Visual Studio for further customisation/development.
I believe it is possible but was looking for some pointers on approach/technique and maybe some links to more information.
I know some MVPs (Todd Bleeker and others) have been working on this in the past, but I have yet to find a definitive solution to the issue.
Also does anyone know if MS are considering improvements to the Workflow designer within the next version of SharePoint Designer?
Here’s a link which might help get you started.