grudie

the boot screen only stops showing the apple startup one windows /osx takes over you have a display ....osx does support and cards i have a 7950 in my mac pro and i have a boot screen (flashed bios) i have yet to find a recent pc card from nvidia that you can just flash a bios onto tho

windows is installable without a bootscreen as is osx if you need to ......you can start the iMac in windows using sys prefs / start up disc without the need for a boot screen and use bootcamp in windows to restart in osx

like windows 7 I'm sure you can't just install it to an external hdd here is some infer tho that may be of use .....but i think you will need a pc as well to do it How to Create a Windows To Go USB Drive

i would just install via bootcamp myself and i wouldn't use 8 but stick with 7

just reinitialised my m15 after it being in storage for 12 months ......popped the battery back in and a quick charge and it fired up as if it had never been boxed away ....now for the 17 and 11 and all the mac stuff :-)