If I understood correctly, if input is 123.45, it should say "NUMBER" else it should say "WORD".
If this is true, why dont you try double.TryParse ? and Int.TryParse?
It will be something like
double value;
bool isNumber = double.TryParse(richTextBox1.Text,out value);
if(isNumber)
{
listView1.Items.Add("NUMBER");
}
else
{
listView1.Items.Add("WORD");
}
Hope that helps
Milind