C#

bool loaded = false;

protected override void OnLoad(EventArgs e){
  loaded = true;
  base.OnLoad(e);
}

public int SomeProperty {
  get {
    if (loaded & DesignMode) dosomethingelse();
    return someint;
  }
}

using System;
using System.Reflection; // For Missing.Value and BindingFlags
using System.Runtime.InteropServices; // For COMException
using Excel;

class AutoExcel {
	public static int Main() {
	
		Console.WriteLine ("Creating new Excel.Application");
		Application app = new Application();
		if (app == null) {
			Console.WriteLine("ERROR: EXCEL couldn't be started!");
			return 0;
		}
		
		Console.WriteLine ("Making application visible");		
		app.Visible = true;
		
		Console.WriteLine ("Getting the workbooks collection");
		Workbooks workbooks = app.Workbooks;

		Console.WriteLine ("Adding a new workbook");
		
		// The following line is the temporary workaround for the LCID problem
		_Workbook workbook = workbooks.Add(XlWBATemplate.xlWBATWorksheet);

...

System.Diagnostics.Process.Start("filename.xls");

private ArrayList tempFiles;

private string GetTempFilename(string extension)
{
   string tempFilename = Path.GetTempFileName();
   File.Move(tempFilename, tempFilename += ("." + extension));
   this.tempFiles.Add(tempFilename);

   return tempFilename;
}

// Make sure this gets attached to the right event.
private void MainForm_Closed(object sender, EventArgs e)
{
   foreach(string tempFile in this.tempFiles)
   {
      File.Delete(tempFile);
   }
}

// In any method, call this.GetTempFileName("tab").  It will return a 
// temporary .tab file, which will be cleaned up on the program's close.