One of the most significant changes to come to PC systems in a decade, PCI Express is a new interconnect technology designed to provide universal connectivity for use as a chip-to-chip and chip to adapter card interconnect. PCI Express architecture provides for extremely high bandwidth at low cost. There are two main reasons to care about PCI-Express:
1) PCI is now an old standard dating back to the early 90's and no longer fits our needs in terms of speed/performance.
2) AGP also is in a similar position as PCI now, and chipset manufacturers are killing AGP motherboard support in favor of the much faster PCI Express interface. This means you are looking at a forced transition in the graphic sector, thus you really don't have a lot of choice in the coming years.
info from
www.gen-x-pc.com