Since it is sql 2000. try the below. It should work but I didn't test it at all.
SELECT DISTINCT dbo.DW_SALESINVOICES_F.Reference AS [Sih.Reference],
dbo.DW_SALESINVOICES_F.InvoiceDate AS [Sih.InvoiceDate],
DATEPART(YYYY, dbo.DW_SALESINVOICES_F.InvoiceDate) AS...