From those of us who worked with the WSP Builder add-in for Visual Studio back in the SharePoint 2007 days, it might not be absolutely obvious how to work with .wsp files in Visual Studio 2010, but it’s more simple than you think – just not so obvious.
Let’s say you have saved a site as a template (creating a .wsp file), but you want to tweak it a little in VS.Net 2010. Instead of opening the .wsp file directly, what you must do is go to File/New/Project. Make sure you select SharePoint 2010 on the left (Installed Templates Category). On the right, you will see quite a few templates available. One of them is ‘Import SharePoint Solution Package’. Browse to your .wsp file and it’s done!
As an extra note, you can even create a .wsp file from a reusable Workflow which was designed in SharePoint designer, save it as a template, and then open it in VS.Net using the ‘Import Reusable Workflow’ template.
All Things DotNet Discussed – Winforms/ASP.Net/SharePoint/WPF