Sis is said to be one of the first chipset manufacturers to release a PCI-Express chipset, and they're set to release it in june/july.
So you might just be able to find one, but if you'll be able to get graphics cards etc for it, is another matter.
The cost might also be improportionable compared to what you get for it.
My guess is that you'll start seeing availability for PCI-Express mobos and gpus this fall for Intel cpu's, with AMD coming along a bit later (christmas perhaps?).