Derived Tables

OK...I know how to write a query to return for example :

All the people that ordered X and Y

but how do I write one for:

All the people that ordered X but not Y?

Thanks,
TreyO yea...this is how i did the first part

SELECT DISTINCT c.Company
FROM Customers as c
JOIN
 (SELECT CustomerID
 FROM Orders o
 JOIN [Order Details] od
 ON o.OrderID = od.OrderID
 JOIN products p
 ON od.ProductID = p.ProductID
 WHERE p.ProductName = 'X') as temp1
 ON c.CustomerID = temp1.CustomerID
JOIN
 (SELECT CustomerID
 FROM Orders o
 JOIN [Order Details] od
 ON o.OrderID = od.OrderID
 JOIN products p
 ON od.ProductID = p.ProductID
 WHERE p.ProductName = 'Y') as temp2
 ON c.CustomerID = temp2.CustomerID