window applcation integrate

please be more specific on question. still following may help


solution 1.
you may right click on solution

then ADD >> EXISTING PROJECT

solution 2.
Add projects in Blank solution.

solution3
if you have to run only application on button click of some form then simply add process to run desired application.
for that try

System.Diagnostics.Process proc = new System.Diagnostics.Process(); // Declare New Process
                proc.StartInfo.FileName = application name;
 proc.Start();

read msdn >>
http://msdn.microsoft.com/en-us/library/system.diagnostics.process.aspx[^]