Yes, it booted, but no pci-x is supported for now and you cannot change your resolution...and color
PCI-X is fully supported by Amithlon, even using the original kernel. It's
PCI Express that isn't supported - or, to be more accurate, most of the chips used on PCI-E graphics cards are not yet supported by the kernel video drivers.
If you get a PCI-E card that has a chipset that's already supported via AGP (like the GeForce FX series) it will probably work fine. I can't guarantee that, however, because the machines I do kernel development work on are all AGP. I don't actually own a single PCI-E card, hence no official support in the drivers till I can get hold of one and a suitable board to plug it into.
I hope to get this sorted soon, because with the next kernel bringing in support for SATA, GigE and most types of on-board audio, PCI-E is starting to look like the main problem in Amithlon's hardware support.