I'm another one suffering from these issues. I think it's possibly connected to having multiple cores. I found this thread on Insanelymac about X2 users, not sure if its still valid for leopard.

http://forum.insanelymac.com/index.php?showtopic=7405&pid=199818&st=120&#entry1 99818

It talks about the use of kernel flags such as idlehalt=0, cpuidle=0, platform=X86PC, fn=3. Also here's a quote from the thread:- "I think the key it is in FSB....OSX loves to run in high FSB."

Edit: Firefox is also crashing with the 'divide by zero' error. Not sure if thats connected at all?

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 Mac OS X 10.6.4 Retail || Intel Core2 Duo E8200 2.66GHz || Gigabyte G31M-ES2L || GeForce 6600 GT 128MB || Realtek ALC883 Audio || Realtek RTL8169 LAN || Samsung SpinPoint F1 1TB HD || Sony Dual Layer IDE DVD RW DW-D22A || Apple Aluminium Keyboard || Mighty Mouse

 MacBook Pro || 2.4Ghz Core 2 Duo || 200Gb HD || 2Gb Ram || NVIDIA GeForce 8600M GT

 iPhone 4 || 16Gb