After searching for several weeks for answers I have finally completed a 100% satisfiable gaming machine. This machine plays games flawlessly Here is my setup: Two 2.66GHz Dual-Core Intel Xeon processors 8GB (4 x 2GB) memory (667MHz DDR2 fully-buffered DIMM ECC) 250GB Serial ATA 3Gb/s 7200 rpm hard drive 16x SuperDrive (DVD+R DL/DVD±RW/CD-RW) ATI Radeon 4850 (PC Version w/ MAC power adapter that goes from card to motherboard)-This card is located in the bottom PCI Express Slot. NVIDIA GeForce 7300 GT graphics with 256MB memory-This card is located in the PCI Express slot above the ATI. Operating System: OSX 10.5 and boot camp Microsoft Vista Business 64bit w/sp1 After you install vista the key is the make sure you install boot camp 2.0 64bit drivers. If you have an early version of a leopard dvd it won't have 64bit drivers. I am told that only the "2008 mac pro dvd's have 64bit drivers". Alternatively you can search for "boot camp 64bit 2.0" and download it off a torrent site. Then after installing the drivers you can then install the "boot camp 64 bit 2.1 update" successfully. After the drivers are up to date install Service Pack 1 for vista. Then finally put your Geforce 7300GT or whichever video card came with your mac in the pcie slot above and put your "PC Video card of choice" in the main bottom slot with the "special order power adapter" attached and install the latest "display driver". NOTE: I don't install the whole catalyst software suite. I tweaked Vista to make it faster using: http://www.howtogeek.com/tag/windows-vista/ I have played many games on Steam, Quake3, Call of duty 4, Spore all without a problem. FAQ: Why did I choose Vista 64bit? I wanted all 8GB's of my memory available. Vista 64bit has more support than Windows XP Pro 64bit. Don't get me wrong I would rather run Windows XP Pro but M$ has a memory cap on the 32bit version and does not support the 64bit version enough for anyone to really care about it. Did you have to change power supplies? No. I have 2 video cards and 4 hard drives and they all run perfectly. Known Issues: Sometimes when exiting Steam games it will show an error on exit. I still haven't figured out a correct method of booting being able to choose which OS to boot to. Sometimes it will just keep booting into OSX.