Ed Beck announced that we have released the English language version of the prerequisite check file for Exchange Server SP1 setup that will allow you to install Exchange 2007 SP1 in a single label Active Directory domain. You can find all the instructions on how to download and install the prerequisite check file at the Exchange Team blog. The English language update can only be installed on English language versions of Exchange Server 2007 but future localized versions will be released in the near future.
As mentioned previously in Exchange Server 2007 SP1 and Single Label Domain Names, we recommend that you move away from single label domains. The next major version of Exchange Server after Exchange Server 2007 SP1 will not support single label domains.