ya eladijaz and omardeth are right, the ultra 400 has nothing to do with RAM support (except that it supports dual channel)
well actually, im not sure about the dual channel thing but i will take their word for it, all i know is i have an ultra400 board that does support dual channel so at least part of the story is right
go with an ultra400, its worth it for the extra support you get. plus, if you dont have a decent sound card its worth getting a board with an mcp-t southbridge, as (unless i am mistaken) this refers to nVidias much renowned SOUNDSTORM chipset, which provides both 5.1 surround and sometimes digital out as well
look for boards that have things like "pro" or "deluxe" on the end
boards such as: gigabyte ga-7nnxpv (or the ga-7n400 pro 2, my board!) , asus a7n8x deluxe or the abit nf7-s are good, and alot of ppl on this forum have good things to say about the DFI LAN party NFII Ultra.
remember, your mobo is the basis of your system. its better 2 spend more on a feature-packed mobo and less on a cpu, than compromise with a mobo so u can get a faster cpu.
note:- all of the abovementioned boards have the mcp-t southbridge chipset. im pretty sure they all support RAID, Firewire, SATA, dual channel ddr etc