Q: When trying to upgrade from 10.6.3 on a Macbook Pro, the update runs into an error before completion.  No info is given about why, is this a known issue?

I'm trying to update a Macbook Pro with 10.6.3.  The latest using Software Update does not complete downloading.  After 475 Mb an error message says it can't connect to the update server.  I tried incrementally updating to 10.6.4. It downloads, starts to install, and just before finshing the install gives a "software error" message and quits.  Is this a known issue, and how can I get around it?