That is the proper host name. The error message you posted is a DNS error. The error means that the N900 didn't get any answer when trying to get the IP address to downloads.maemo.nokia.com. Ther are either network issues between your N900 and Nokia's DNS servers. Or Nokia's DNS server are having some issues.

In short, the problem isn't on your end. You can't fix it. You can try to open a ticket with your ISP. They should be able to figure out very quickly (when they get to it) if it's a network connectivity problem. I haven't seen the anyone else complain that Nokia.com, et al is down. So I'm gonna guess it a network connectivity or routing issues of some sort.