How can I convert my application from Visual Studio 6.0 to Visual Studio 2008?
I think that conversion is builtin. There is a conversion wizard that helps you, so just try opening your solution in the latest studio version you have.
Probably buildin in VS. Recently i converted a project from VS6 to VS2005. So to 2008 won't be a problem.
I just opened a client's VS 6.0 C++ application in VS2008 a couple of days ago. The conversion was completely automated (via a wizard). Totally painless (although this was a simple test application).
Remember that converting to a VS2008 project is a destructive process -- VS does not automatically backup your VC6 project. You will be better served to create a copy and work on that, so that even in case something goes wrong you have a way to revert back.
Conversion from VS6 to VS2008? I think you're probably converting a VB app, or are you?
The Conversion Wizard (File->Open) will automatically convert the older project types to new ones. Remember to keep a backup when you use it.