Upgrade to Vista or Office 07 @ Microsoft for $24.55
So you can upgrade Office 03 standard to Office 07 for and XP Pro Full for $24.55 which is pretty good.
There's T&C involved so read em but if you bought your boxed copy between 26/10/2006 to 28/02/2007 go for it. You need to mail it in before the 31st March though.
No cashback on this obviously.