Hello all, I have two PS3's in front of me, one is running HDMI and the other regular video and set to 4:3. The HDMI plays borderlands vertical split, and the other plays horizontal. I've been trying to find an answer to this for a while and when I hooked up the other PS3 and put in borderlands I got my answer. So there you go. So if you want it horizontal splitscreen you must lose HDMI. Hope this helps you!