Sorry to resurrect this thread, but I stumbled over it while searching for timing information. Just wanted to say that if you guys are struggling with fixed timing, consider buying my Time module - it makes it all pretty painless. Here's some sample code that demonstrates how fixed time stepping would work:
http://www.pixelfist.com/samplecode.php?modname=time&id=2
http://www.pixelfist.com/samplecode.php?modname=time&id=2