I found a solution that worked for me, in XP, and didn't require me to downgrade my drivers, which is nice.
Simply put, I just dropped the older OpenGL dll's into EPSXE's folder.
(I used the ATIOGLx2.dll and ATIOGLXX.dll from catalyst 7.11, not sure if I needed both or not)
It seems, for me at least, to have fixed the problem without having any other effect. I didn't change anything else and the triangles just went away. Didn't even need to reboot.
Don't know if anyone else has pointed this out, if they have just ignore this message...
