After June 30, you will likely no longer be able to buy Office 2003; you must buy Office 2007 licenses. If you have volume licensing, then you can actually downgrade to Office 2003 from Office 2007. That is not an option for off-the-shelf or OEM licensing.
This might be a good time to have a serious look at Office 2007. I had serious concerns about the new user interface, particularly in Word. However, after a couple of days, I got used to it and found I could do things much faster with O2007. I’ve been using Office 2007 at home since the public beta programs early last year. I’m currently using Office 2003 at work and I’m struggling to get used to the old GUI J
Note: MS will stop shipping O2007 on the 30th. Some boxed copies will likely be sitting in retailers and in warehouses which will still be available to buy off of the shelf.