I published my first article on an ISA/SBS issue @ www.isaserver.org after having been through the frustration of learning that the SBS team messed up the packet filter that was supposed to allow syncronization with an external time source. I undestand that there is now also (finally) a kb article on the subject. Although our solutions are similar I like mine better because I simply make the correction necessary to the existing NTP packet filter, while the kb article leaves the misconfigured packet filter in place and instructs you to create a new one. The way I look at it, there are enough protocols definitions and packet filters in ISA already, I don't need misconfigured ones lying about in there.
How to Synchronize SBS2003 Premium with an External Time Source