In a catalog db, where each product has a classID, and each class has a parent ClassID, up numerous levels, and one must generate a list of all parent ClassIDs for a specific product in the quickest, most efficient manner, what would that manner be? I have tried cursors (not fast), while loops, etc. but these take longer that 2 minutes to run (the list is long and a little complicated). I have run through the index tuner with a load file, but the indexes seem to be OK. Consider the tables as the following:

CREATE TABLE [dbo].[Class] (
[ClassID] [int] IDENTITY (1, 1) NOT NULL ,
[ClassDescrp] [varchar] (50) COLLATE SQL_Latin1_General_CP1_CI_AS NULL ,
[PrntClassID] [int] NULL
) ON [PRIMARY]
GO

CREATE TABLE [dbo].[Product] (
[ProductID] [int] IDENTITY (1, 1) NOT NULL ,
[ProductDescrp] [varchar] (50) COLLATE SQL_Latin1_General_CP1_CI_AS NULL ,
[ClassID] [int] NOT NULL
) ON [PRIMARY]
GO

ALTER TABLE [dbo].[Class] WITH NOCHECK ADD
CONSTRAINT [PK_Class] PRIMARY KEY CLUSTERED
(
[ClassID]
) ON [PRIMARY]
GO

ALTER TABLE [dbo].[Product] WITH NOCHECK ADD
CONSTRAINT [PK_Product] PRIMARY KEY CLUSTERED
(
[ProductID]
) ON [PRIMARY]
GO

ALTER TABLE [dbo].[Class] ADD
CONSTRAINT [FK_Class_Class] FOREIGN KEY
(
[PrntClassID]
) REFERENCES [dbo].[Class] (
[ClassID]
)
GO

ALTER TABLE [dbo].[Product] ADD
CONSTRAINT [FK_Product_Class] FOREIGN KEY
(
[ClassID]
) REFERENCES [dbo].[Class] (
[ClassID]
)
GO

I would like a simple select statement to do the task, but am not sure how to put that together.
All help is greatly appreciated!!