Transitioning from Visual Studio 2008 SharePoint or VSeWSS Projects to Visual Studio 2010
If you develop SharePoint solutions using Visual Studio 2008 or Visual Studio 2008 extensions for Windows SharePoint Services 3.0 (VSeWSS), then you can easily create SharePoint applications in Visual Studio 2010. However, when transitioning to Visual Studio 2010, there are differences in the feature sets and functionality that you have to understand.
Visual Studio 2008 provides two SharePoint project templates: SharePoint 2007 Sequential Workflow and SharePoint 2007 State Machine Workflow. These templates still exist and you can continue to create SharePoint 2007 workflow projects in Visual Studio 2010 using them. However, these workflow projects cannot use any of the new SharePoint 2010 workflow functionality or features. To access the new functionality, use SharePoint 2010 workflows.
You can open and edit an existing Visual Studio 2008 workflow project in Visual Studio 2010 and recompile it while still maintaining binary compatibility. You cannot, however, add existing Visual Studio 2008 workflow projects to Visual Studio 2010 solutions. One way to work around this is to create a new Visual Studio 2010 workflow project, manually copy and paste the code and workflow files into the project, and then correct any errors.
For more information about the SharePoint 2010 Visual Studio templates, see SharePoint Project and Project Item Templates.
Visual Studio 2008 applications that use the VSeWSS are not directly compatible with Visual Studio 2010. For more information about how to upgrade SharePoint solutions, see Redeploying Customizations and Solutions in SharePoint Foundation 2010 and SharePoint Server 2010.