I think some Intel PCI cards don't work, from memory. You also need a custom parameter for booting on most Intel motherboards.
I actually think that for just file serving for a few users and low-volume traffic for emails and maybe a website, that the configuration might be overkill. I have a couple of customers using 3Ghz/1Gb machines very happily with 3-4 client computers. The only important thing is hard drive capacity and backup availability.