If you were using Visual Studio 2005 for your web project and wish to convert to Visual Studio 2008, all you need to do is:
1.Start Visual Studio 2008.
2.Click File -> Open website... .
3.Choose the folder with your web project on the disk and click OK.
4.If you're asked if you wish to upgrade the project to a newer version of .NET Framework and Visual Studio, click Next and go through the wizard.
You may receive a compilation error saying there are different versions of the System.Web.Extensions.dll library in the Global Assembly Cache (GAC) and a temporary folder. In this case, you need to locate the file bin/System.Web.Extensions.dll in your web project and delete it.