John,

Weldment sketches should automatically update for you and so should everything else within the assembly. Are you working with large assemblies? If so, there is a Tools-Option in SW 2006 that suspends automatic rebuild when working with large assemblies. I think this option is in earlier releases as well.

Look at your settings in Tools-Options-(System Options Tab)-Assemblies. There you will be able to set the threshold of components before it is considered a large assembly and select options you want or don't want when the large assembly mode is active.

Best Regards,
Jon