Something weird has been happening with my PowerMac G5, and at first, I wasn't sure what the hell was going on.

Situation 1: I leave the G5 alone and it goes to sleep, hours later I'm roused from sleep (or Sarah is, who THEN rouses *me* from sleep) only to have the Mac completely unresponsive and necessitating a hard shutdown.
Cause: Unknown

Situation 2: I'm working on a variety of tasks (syncing ipod, syncing PDA, updating blog, cleaning up media, etc), and I'm met with a grayed out screen that tells me I need to shut down immediately by pressing the power button for five seconds, and if I don't the fans...the get loud.
Cause: Unknown

Now, I'm familiar enough with *nix stuff to do some moderate troubleshooting and problem identification, and what I could gather was that this was a kernel panic, but no real cause was established after further inspection.

Doing what I do, I figured I'd troubleshoot the crap out of the problem:

1) Remove ALL peripherals (except keyboard/mouse)
2) Does it shut down?
3) No
4) Add peripherals one at a time (sans USB hub), starting with iPod Shuffle 1st Gen, use it as normal, then remove
5) Does it shut down?
6) No
7) Add Wacom tablet, use as normal, then remove
8) Does it shut down?
9) No
10) Add external hard drive, use as normal, then unmount
11) Does it shut down?
12) No
13) Add USB hub, use as normal, attach/detach other peripherals through it
14) Does it shut down?
15) No

Well shi...hang on!

16) Attach PDA, load up Missing Sync 4.0.2, run a sync, disconnect...
17) Kernel Panic.

Thing is, this doesn't seem to be happening to JUST me, and my set up is completely different from that of a lot of other folks experiencing this. And Missing Sync doesn't seem to be the wax seal here, either, but it IS happening to others with Missing Sync 4.0.2 and Leopard 10.5.1.

Is this an Apple problem? Because I can't pin down whether this happened prior to my starting to utilize my PDA via my Mac (the timing is a little hazy).

I'm hoping for updates to both Leopard and Missing Sync and a number of other things soon, which may help to alleviate the problem entirely. In the mean time...very carefully do one thing at a time :(
8) Does it shut down