XNA bool IsSpecialKey(Keys key)

public bool IsSpecialKey(Keys key)
{
 // All keys except A-Z, 0-9 and `-\[];',./= (and space) are special keys.
 // With shift pressed this also results in this keys:
 // ~_|{}:"<>? !@#$%^&*().

 int keyNum = (int)key;

 if ((keyNum >= (int)Keys.A && keyNum <= (int)Keys.Z) ||
  (keyNum >= (int)Keys.D0 && keyNum <= (int)Keys.D9) ||
  key == Keys.Space || // well, space ^^
  key == Keys.OemTilde || // `~
  key == Keys.OemMinus || // -_
  key == Keys.OemPipe || // \|
  key == Keys.OemOpenBrackets || // [{
  key == Keys.OemCloseBrackets || // ]}
  key == Keys.OemQuotes || // '"
  key == Keys.OemQuestion || // /?
  key == Keys.OemPlus) // =+
 {
  return false;
 }

 return true;
}