Forms 9i doesnt have a ifrun90.exe, just like previous versions. They have been deprecated. From 9i you only have the web version that runs as an applet. If you just want to test your forms from your system, start the oc4j instance in the forms start menu, and from the forms designer click the run button (green one).
If you want to set it up completely you will need Oracle 9ias rel 2 and above. I would highly recommend going straight to 10g as they have just the forms/reports server installation which is fairly easy compared to the complete installation.