At the Computex Exhibition ATI will launch two new PCI Express cards, namel the RV380 based Radeono X600 , and a RV370 based Radeon X300.
The X600 (RV380) is a mainstream card that will fit in the sub $200 market, it is built on the 130nm production process. The X300 (RV370) is ATI's first 110nm chip, which is going to take place in the sub $100 market. Both are PCI Express compatible, and ATX based.
As for the R423/X880 XT, this card won't be introduced at this show as far as we know. The PCI Express era starts in June and will dominate over the next few years.