I've spent two days to finally successfully installed El Capitan + Windows 10 on my old Mid-2010 Macbook Pro (Model MC374).

  1. The key point  to install Windows 10 on MC374 is that you have to boot the installation under traditional mode instead of EFI, otherwise graphical card driver will crash. Have been struggling with this problem for a whole day before I came across this discussion on Apple forum;
  2. In order to boot the traditional way, I had to use DVD. USB stick doesn't work because it can only boot EFI mode, or maybe I don't know how to do it. The SuperDrive hasn't been used for several years I guess, and it simply didn't work at first, complaining " error burning disk image: the disk drive didn't respond properly and can't recover or retry". I'd done some housework by following this with alcohol and dishcloth, and it did work!
  3. El Capitan's BootCamp assistant supports USB-less Windows installation, which means it can use an ISO file instead of physical USB stick or DVD. But... old model Mac are not supported. And because the Windows to install is 10 instead of 7, the assistant won't even do the partition work, so have to do it manually;

After so many years in IT industry, and installing OS is still one of my major work. So pathetic.