I have my Dell WS 490 listed on eBay for sale/auction.
It was built per this thread.
From the ad:
Computer: Dell Precision WS 490 dual boot
This is a Dell Precision Work Station 490 (Dell's enterprise line), with dual quad core Xeon cpus at 2ghz for a total of 8 cpu cores. It has a 320gb sata hard drive, 4GB ram, dvdrom drive, gigabit ethernet via a new Rosewill pci card and a new 1GB ATI HD 6450 video card with DVI/HDMI/VGA ports. I built this for my Dad as a gift to replace his dead G5, but he informed me (before knowing I'd built it) that he had no interest anything besides a Mac branded box. I've kept it here on my desk since December, booting it up to play with it- but honestly have no use for it, so it's up for sale. It has kernel panic'd three times- ONLY when automatically booting after a Windows XP restart into the Mac OS, but boots fine after a power off or pausing at the bootloader screen. That is the only thing it's done out of the ordinary and it does it early in boot.
It's using Chimera boot loader to choose the OS immediately after posting. It will automatically boot into either OS of choice, or you can hit any key and it will pause and allow the user to choose the OS. I've only tested it for the standard functions using applications that come with each OS, but there hasn't been any issues so I don't foresee any with other OS compatible software. The Windows XP COA and Mac OS X 10.6 Snow Leopard installation disk are included. 10.6 is the last version of Mac OSX that will allow you to run older powerPC apps (using the OS installed Rosetta) which is nice for flexibility. Audio out is from the front headphone port in Mac OS. I have not tried the audio on the ATI video card's hdmi port (don't have something to test it with easily) but it is showing up in the VooDoo HDA control panel (pic below). Video out is confirmed working both the DVI and HDMI ports of the ATI video card under both OS. The case has a couple of scratches and bumps, but nothing out of character for a used computer IMO. Doesn't included any peripherals- what you see in the photo is what you get. Flat rate shipping of $32 to the lower continental U.S. only.