I might try to get this running in the coming month. Will be a really cool project to turn that laptop into an instant gaming desktop, but I don't know how I'll do it with completely free software.
I currently main a T440p, so it'll be like going back in time a tad when I flash the T400 with either Libreboot or Coreboot and solder the wire on the motherboard allowing it to accept a Quad Core Q9100 cpu in its socket.
I've recently seen Tripcode's video on this and am quite excited to give it a try.
What kind of games should I try out on this setup, once I have it ready?