MCSE won't expire until those technologies aren't used anymore. But they are already leaning towards not supporting the MCSE. Just look at the exams you have to take for it, server 2000 and 2003, older technologies (still used widely by companies but will become less used within the next year). The new one is the MCITP which involves four certifications out of server 2008 and one of an OS technology (either xp or vista). While they still support the MCSE they definately are wanting people to move into the new certification route of MCITP.
Long story short almost every certification you take will be outdated and unsupported at some point. As computer and IT professionals we cannot expect a company to support exams that are 5+ years old in an age in which the hardware and software we use change on a monthly, sometimes weekly basis.
http://www.microsoft.com/learning/en...mcse.aspx#tab2