Misc startup/kernel panics on iBook G4

I've been trying to diagnose multiple kernel panics and startup issues on one of our 1.42 GHz G4 iBooks. Currently, the problem is that when I press the power button, I hear the startup chime but the screen does not work. I have to hold the power button to shut down. When it does boot, and the screen works, it will work for a while but then kernel panic.
I've run all sorts of diagnostics, including the Apple Hardware Test (which it passed).
I've reinstalled Tiger (erase and install).
I have an external hard drive with a troubleshooting partition of Leopard which the 'Book will boot from.

Today I managed to capture this report:
Interval Since Last Panic Report: 2432 sec
Panics Since Last Report: 2
Anonymous UUID: 76E06AD4-DDCE-46F3-AFC0-4A312904B67B

Mon Apr 12 16:17:15 2010
panic(cpu 0 caller 0x000A8C00): Uncorrectable machine check: pc = 00000000006B352C, msr = 0000000000149030, dsisr = 42000000, dar = 00000000E00EF000
AsyncSrc = 0000000000000000, CoreFIR = 0000000000000000
L2FIR = 0000000000000000, BusFir = 00000000ff000000

Latest stack backtrace for cpu 0:
Backtrace:
0x000954F8 0x00095A10 0x00026898 0x000A8C00 0x000A7E90 0x000ABB80
Proceeding back via exception chain:
Exception state (sv=0x3C293000)
PC=0x006B352C; MSR=0x00149030; DAR=0xE00EF000; DSISR=0x42000000; LR=0x006C8078; R1=0x21FBBD30; XCP=0x00000008 (0x200 - Machine check)
Backtrace:
0x0027D47C 0x006C8078 0x002D1B8C 0x002D0A54 0x000A9714
Kernel loadable modules in backtrace (with dependencies):
com.apple.iokit.AppleAirPort2(405.1)@0x689000
dependency: com.apple.iokit.IONetworkingFamily(1.5.0)@0x5b6000
dependency: com.apple.iokit.IOPCIFamily(1.7)@0x48d000
Exception state (sv=0x37B31000)
PC=0x00000000; MSR=0x0000D030; DAR=0x00000000; DSISR=0x00000000; LR=0x00000000; R1=0x00000000; XCP=0x00000000 (Unknown)

Kernel version:
Darwin Kernel Version 8.11.0: Wed Oct 10 18:26:00 PDT 2007; root:xnu-792.24.17~1/RELEASE_PPC

Anyone know what this report is telling me?

Thank you.