settings problem in C#

i'm trying to save a setting so that on startup, my client will automatically load a world. There is a list of all the worlds in a listbox, but i can't figure out how to save the selected world in the listbox to my settings.

here is what i have, it doesn't give any error, but it doesn't work.

Code:

Properties.Settings.Default.startupworld = (int)val(combostartupworld.SelectedText);

the val thing that I used is this: - creds to flaming idiots

Code:

		public static double val(string s)
		{
			double D;
			double.TryParse(s, out D);
			return D;
		}