Thanks for the heads up.
For now, Media Center asks for administrator priveleges on Vista. Since Media Center runs fine with a guest account on XP, we may be able to change this in the future. Does the release version of Vista add a way to say "Always allow administrator priveleges?" so it isn't annoying?
We're still using RC2, and we need to click OK four times to do anything -- even something as simple as copying a file. I really hope they tone this down, because it's the "cry wolf" problem. I'm so used to clicking OK that they could be warning me my hard drive is being formatted by a virus and I'd still mindlessly click OK.
As for the problems you're mentioning, I'm not sure on either of them. MC uses standard file access, so if the NAS isn't working, it may be a NAS, driver, or OS thing.