After reading the previously published tip about hiding iMovie while rendering, I decided to see if there were any changes with iDVD. I started 'top' running after iDVD began encoding, and noticed two processes using most of the CPU time: EncoderSer and iDVD. Both were using around 50% CPU on a DP500. After hiding iDVD, it's usage dropped to 2% and the EncoderSer jumped to 163%.
Encoding went much faster!
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http://hints.macworld.com/article.php?story=20020207221114486