Finally, the moment of truth came to fire up the beast.
I stuck my flashed FX5200 in it, hooked up a monitor, and held my breath while I hit the power button. It booted to the Apple logo, and then I got a kernel panic during boot.
I tried the usual suite of troubleshooting-reset the PRAM and PMU, and even installed a new PRAM battery. I booted into single user mode and ran FSCK-it reported no error.
Finally, I pulled the FX5200 and dropped in a Rage 128. It booted right up. I guess that-for whatever reason-it just doesn't like the FX5200. I've used it in a couple of G4s, and it's worked fine, so I'm not sure what's going on. In any case, since my ultimate plan is to run it headless, this really isn't an issue-the Rage 128 is enough for me to get it set up. If I were going to do any serious work on it, I'd pull the 9200 out of my B&W G3, but don't see any immediate need to do that.
By the way, it currently has two 80gb HDDs. I need to pull one of the sleds and look at it-I'm assuming I can put larger/faster drives in the sleds I have, but would appreciate confirmation on this.
I'm running software update now.
I'm going to watch Ebay like a hawk, and hopefully I'll be able to pick up Leopard Server for a reasonable price.
One other thing-someone earlier mentioned these being loud. Having used the IBM servers a fair bit, I have to say that I think computer volume is fairly subjective. Under decent load now, the Xserve is quieter than any of my IBMs at idle. The IBMs run all 10 fans at full blast for a few second on booting, and could easily be mistaken for a helicopter taking off. The Xserve is probably no louder than my souped-up Quicksilver(and quieter than that same G4 with the leaf blower on the front running).
But, in any case, Kentucky is playing Georgia so any further experiments are going to have to wait. We're supposed to get snowmageddon round two tomorrow afternoon into Thursday, so I hopefully will have some more time then to play around with it.