it is not possible to install oracle on rhel4 server using fedora5 xorg server over ssh forwarded X11 connection, since they are different versions. really, i'm getting blank java window of oracle installer on my fedora5. and if i run installer locally on rhel4 or try old non-secure X11 network connection (export DISPLAY=fc5:0.0) or using port forward over ssh (not x11 forwarding) - it goes just fine. i wander what changed so much in xorg (rhel4 using xorg-x11-libs-6.8.2-1.EL and fedora5 X Window System Version 7.0.0 [xorg-x11-server-Xorg-1.0.1-9.fc5]). and yes, xclock runs well.

ps: if you don't need commercial redhat support, stick to centos linux for your server.