After spending all morning installing and running Ad-Aware, emailing Dana to find out that no, my domain doesn't expire until November (I hadn't thought it was even close!), etc, etc, I find that the problem
with www.ambercastle.net seems to be localized to this LAN. jilly_bear sees the same interloping page that I do. Chris suggested that the company might have blocked the domain and then this
thing is coming up in the place of the "blocked site" error. It seems as likely as anything else, although I can't see why the domain would be blocked. There's nothing offensive there!

On the other hand, gratuitous plug for dissolvedgrrl's webhosting service: I can't imagine getting better personal assistance and immediate response when I had an apparent problem. Thank you Dana!