I know this not what we want to do or what we like to do. We all like to do the upgrade. However there are instances where you have a VS solution file that you created in VS 2010, and when you try to open it in a machine where only VS2008 installed, you cannot open it. I had this problem today and it is quite easy to resolve this issue.
Before you do anything backup your files. Open your solution file in your favourite text editor and change the below Format version to 10.00 and # visual studio version to 2008
Below tool ToolsVersion to 3.5 if you have .NET 3.5 installed.
That’s it save your file and you can open your project and the solution in VS2008. . I hope this tip will be handy for you.