You can declare a function as:
private void sendScreenMessageTo(int army, string msg,
params object[] parms)
then array for the parameters will be generated automatically, the call will be easier to look:
sendScreenMessageTo(myarmy, "I am at grid {0}, {1}", xpos, ypos);
Also, lowercase first letter in class or function name is Java style, not C#.
Microsoft C# Code Design Guidelines.