Samsung PC1066 is not available at the present time. I know there are a few sites around claiming to be selling Samsung PC1066, but it reality, it is just remarked PC800. Avoid it like the plague I personally would go for as much as you could afford. I chose the Kingston 256mb PC1066 modules. They were $128 a piece, and gave 512mb of memory. I personally don't see no need of 2gb of system memory, but hey, if it floats your boat, then go to it I am sure that 512mb modules will be available soon. All depends on the yields the memory chip manufactures are hitting. And yes, you do need "2" of the same size and speed chips.
The 8IHXP is a SWEET motherboard! Yes it is limited to only 156 on the FSB, but this thing smokes! I am running a 1.8A @ 2.4 and its happy as can be! Ran Prime95 for a little over a day with no errors. I wish the bios would have been an Award, but I am use to the AMI bios' back from the MSI KT266 days. It has been rock solid, without any issues to date. Everything installed without a hitch (WinXP Home), including all the devices and drivers....