Having taken a quick look at the systrace package it appears to install a mach_kernel.test. It then uses a script to set this to be the boot kernel in nvram. I also see that this tool is curently not maintained and appears to be a 10.2.x kernel, not good if you've installed this on 10.3.x
The good news is that it doesn't replace the original kernel so you should be able to change the open firmware setting to point back to the original kernel. I think zapping PRAM should do the trick, but you may need to log into open firmware and reset the nvram if not. To zap PRAM turn on your iBook and then hold down the cmd-option-p-r keys together. Apple says to wait for a second chime, I like to hear at least one more just to make sure :)
Apple Instructions on Resetting PRAM
Hopefully, that will do the trick and you'll be able to get back in and uninstall systrace. Let us know how you get on.