Sometimes installing the Oracle Jinitiator just doesn't go through properly. I recently had the experience of trying to install it several times, and it crashing out right at the end.
Assuming that it had probably done all the good bits earlier in the install, I ignored the error and fired up the URL, and up popped the Oracle window!
However, at the bottom of the windows were yellow warning bars, and I could not cut and paste into it.
After hunting around on the internet for a while, I worked out that it was something to do with the identitydb.obj file, so rather than get deep down into the hows and whys, I just copied the file from a working machine over onto the new PC and after a quick restart of IE, everything was fine once more!
You can fine the file in c:\program files\oracle\identitydb.obj
I hope this helps you and your Oracle woes... if so, please click on one of the ads on this site to show your appreciation.