I apologize for contributing to the problem. It just rubs me way the wrong way when people completely lacking evidence to support their beliefs start flinging their "PowerPC IS THE ONE TRUE GOD" dogma around. It's a personal failing of mine.
As I noted in the bottom in my last post... I find it curious that (as you describe it) the crashes tend to come shortly after booting. I also think it's interesting, looking at the kernel panic, that it references the "kextcache" process. Do you have any "extra" hardware hooked up to this thing, like an external hard drive, USB scanner, anything, that might be failing to initialize properly and panicking the machine? Do you have any extra PCI cards, like a USB card? And finally, are you using Airport? I've seen both bad USB devices and bad Airport cards cause panics. And I guess to add to that, I've also seen a panic from a dying hard drive.
I also repeat... do you have the original disks, specifically the hardware test/diagnostics? (Depending on the vintage of the Mac that may be a stand-alone CD, or it may be on the "Restore DVD". Hold down the option key and select it from the menu.) A few cycles of the memory test should root out bad RAM. If it's a built-in hardware device that's failing it may catch that as well.