A very nice setup, but if it's for gaming (which I can only assume it is, otherwise, you'd be way over the top), Vista 64 -bit has a lot of issues with many games. If you are only looking to play new games, that shouldn't be a problem though.
If you want to save a little money, get a cheaper version of the X-Fi. The extrea onboard RAM does absolutely nothing. I have the Fatality edition, and only a few games support it, and there honestly isn't much of a difference IMO. Vista Ultimate is not a must either, I also forked over the extra money for it, but I really can't say that I use any features that weren't already in Home Premium or Business. I wish MS would fix Media Center so it didn't run so slow (rather, it runs fine, but due to the animations, it takes ages to get anywhere using the interface) - at least compared to XBMC or similar. You probably won't be able to use all cores for a while, but given the low CPU prices at the moment, I see no reason to get a dual core.
Some people also prefer a non nForce chipset, as it has had problems earlier. I have no idea whether these are resolved by now, but it's worth looking into.
Otherwise, good choice. ASUS is a greater brand, and overclocking is made almost painfully easy. I don't know how well the RAM perform if you're planning to overclock though.
