One suggestion I've received is that you just do:
regsvr32 rsabase.dll
Alternatively, I understand that you can install SP3 after IE4, but you have to know which files to skip... don't ask me, because I don't know which.
If you're desperate, you could find out, providing you've got enough time. I'm told that when you install SP3 after IE4, it'll notice that the files have already been updated, and will ask you whether you really want to update each again. With time, you could determine which SP3 files you can reinstall without nuking your system. This may come as a shock, but I haven't decided to repeatedly kill my system in order to determine which are safe. Like I said, if you're desperate...
You're probably after something more helpful, since your system is already toast anyway. Try this:
Some other stuff that might be useful: