"You Must Restart Your Computer" Error Message on Startup

So my wife started up our iMac (24"/2.8/2 GB/500GB running 10.5.4) this morning and got a message that said You Must Restart Your Computer while holding down the power button. After successive tries, this did nothing, even with no items plugged in. Neither did resetting the PRAM. We also ran a basic and extended hardware test, which showed everything was fine.

We were able to get it to start up in safe mode. A box then appeared and said that OS X had crashed, and provided the following details. Does anyone know what this means, and can offer some advice? It's a bit out of my range of knowledge. The only thing that we installed recently was Microsoft Silverlight yesterday to watch the Olympics on NBC.com. Thanks much for any help you can offer!

Mon Aug 18 09:33:04 2008
panic(cpu 1 caller 0x001694C6): "vm_map_unwire: entry is unwired"@/SourceCache/xnu/xnu-1228.5.20/osfmk/vm/vm_map.c:4110
Backtrace, Format - Frame : Return Address (4 potential args on stack)
0x2e913df8 : 0x12b0fa (0x4592a4 0x2e913e2c 0x133243 0x0)
0x2e913e48 : 0x1694c6 (0x45c20c 0x3727a000 0x0 0x2e913f0c)
0x2e913f28 : 0x5be328 (0x3728a000 0x0 0x0 0x0)
0x2e913fc8 : 0x19ebdc (0x0 0x0 0x1a20b5 0x4009128)
Backtrace terminated-invalid frame pointer 0
Kernel loadable modules in backtrace (with dependencies):
com.apple.BootCache(30)@0x5bc000->0x5c0fff

BSD process name corresponding to current thread: kernel_task

Mac OS version:
9E17

Kernel version:
Darwin Kernel Version 9.4.0: Mon Jun 9 19:30:53 PDT 2008; root:xnu-1228.5.20~1/RELEASE_I386
System model name: iMac7,1 (Mac-F42386C8)

 

Yes, although none of them were particularly helpful, since I pursued most of the steps suggested. I hoped posting the log would enable someone with more knowledge of this stuff than me help to know what exactly it is.

 

Yes, we unplugged everything and tried to start it up while plugged into another outlet -- no joy.

 

OK, I will give this a try... will boot-up times ever return to normal if I do this?