Check your applications and be sure that they run on Windows XP x64. There are a handful of 32-bit Windows XP applications that wouldn't work on x64. Also, if there is no x64 version of your application then running the 32-bit version on Windows XP x64 (assuming that it is compatible) will offer little performance improvement, if any at all.
That being said, I like ASUS boards. I've got a K8N and an Athlon 64 3000+ (socket 754). Runs like a champ and never had a hiccup. But nowdays most people will want to opt for a socket 939 board with PCI-E slots instead of AGP. While the 939 boards and CPUs used to have a price premium over the 754, they have come down in price quite a bit. Socket 754 is now for the value line of AMD CPUs and 939 is the platform standard.