Sometimes is very usefull for testing purposes to create a VS2005 instance, and them use that instance to have access to the DTE API stuff.
So, here is a code snippet to create a VS2005 instance and to open a solution:
Type t = Type.GetTypeFromProgID("VisualStudio.DTE.8.0");
DTE dte = (DTE)System.Activator.CreateInstance(t, true);
try
{
dte.Solution.Open(@"C:\Temp\Temp.sln");
//Wait some seconds to let VS open the solution
System.Threading.Thread.Sleep(5000);
}
finally
{
dte.Solution.Close(false);
}