By 'disabling' a range of days I presume you would want to prevent users from modifying existing items, creating new items or moving other items into the disabled range. To achieve this you will have to handle the Calendar.ItemModifying and Calendar.ItemCreating events. You can inspect the new start and end date of the item being modified or created and confirm or reject the operation if the item destination doesn't meet particular requirements. The following code prevents users from moving or creating items in the past (assuming that the current time is 31th of July, 2007):

// Calendar.ItemCreating event handler
private void calendar_ItemCreating(object sender, ItemConfirmEventArgs e)
{
    if (e.Item.StartTime < DateTime.Today)
	  e.Confirm = false;
}

// Calendar.ItemCreating event handler
private void calendar_ItemModifying(object sender, ItemModifyConfirmEventArgs e)
{
    // Do not allow items from the past to be modified at all
    if (e.Item.StartTime < DateTime.Today)
    {
	  e.Confirm = false;
	  return;
    }

    // Do not allow items to be moved to the past
    if (e.NewStartTime < DateTime.Today)
    {
	  e.Confirm = false;
	  return;
    }
} 

Meppy