Correlated Sub Query

I'm using Transact SQL for SQL 2000 and I'm having difficulties with a correlated sub-query.

I have a table called 'Results' like this...

Company_ID Product Spend Flag_Top25
1 Product A $100
1 Product B $250
1 Product C $450

I want to create a flag to identify if a companies spending for each product is within the Top 25% of spending within the product category across all products.

For example, the code below would identify the Top 25% of Companies with spending on Product A.

SELECT TOP 25 PERCENT Company_ID
FROM Results
WHERE Product = 'Product A'
ORDER BY Spend DESC

I'm trying the following correlated sub-query to get this done and it is not working.

UPDATE Results A
SET A.Flag_Top25 = 'Top 25% Customer'
WHERE A.Company_ID in (
SELECT TOP 25 Percent B.Company_ID
FROM Results B
WHERE B.Spend > 0
and B.Product = A.Product
ORDER BY B.Spend DESC
)