Firstly, I have NO IDEA which forum this belongs in, as it's kinda to do with Mac Hardware, and Software, but then also kinda not to do with Mac at all, more Windows...so Mods, please feel free to relocate where you see fit! Here's the sit: I have a Macbook running OS X. It had a 120GB HDD. I bought a 250GB HDD and an external USB enclosure. I put the 120GB HDD into the enclosure and the 250GB HDD into the Macbook. I'd like to be able to run OS X as normal from my internal HDD, but also run Windows XP from the external HDD. I've found that it IS possible to run XP from a USB device on Macbook, as instructed here: http://forum.onmac.net/showthread.php?t=1015 and improved upon here: http://tubeshards.wordpress.com/2006/12/05/install-windows-to-a-macintosh-usb-drive/ So I've made a custom XP USB install CD I've installed ReFit I've formatted my external drive to NTFS I've disconnected my Macbook's internal drive I've successfully booted the Macbook from the XP install CD... Unfortunately that's where I'm stuck in my tracks. After the XP text-mode installer starts up, it shows me all the usual screens; the EULA, the 'which partition do you want to install Windows on?' screen (which detects my external USB HDD fine, with partitions). However, when I select a HDD on which to install, it tells me that it can't install to this hard drive: I know it's asking a bit to want to install Windows XP on an external drive for use with an Apple computer :-D but it is possible, as others have managed to do it... Does anyone have any ideas what the problem might be?