Assuming you don't have SQL2005 and therefore the PIVOT function you could always resort to

DECLARE @display TABLE(ID INT IDENTITY(1,1),Display VARCHAR(50))
DECLARE @lRow TINYINT
SET @lRow = 0

DECLARE @NewRow VARCHAR(50)

INSERT INTO @display (Display) VALUES('|---+---+---|')

WHILE @lRow IS NOT NULL
BEGIN
SELECT @lRow = MIN(RowID) FROM dbo.sudoko WHERE RowId>@lRow

IF @lRow IS NOT NULL
BEGIN
SET @NewRow=''
SELECT @NewRow = COALESCE(@NewRow,'')+CAST(CellValue AS CHAR(1))
FROM dbo.sudoko
WHERE RowId=@lRow

SET @NewRow = LEFT(@NewRow,3)+'|'+SUBSTRING(@NewRow,4,3)+'|'+RIGHT(@NewRow,3)
INSERT INTO @display (Display) VALUES('|'+@NewRow+'|')

IF @lRow %3 = 0
INSERT INTO @display (Display) VALUES('|---+---+---|')

END
END

SELECT Display FROM @display