I know this sounds weird, but why is my computer still working?

I just installed Mac OS X 10.5.3, it finished the install but then a message popped up saying that the install didn’t work because of conflicts in ”/”. So I let it restart and log-in and now Im on 10.5.3, even though it said it failed to install. First off, WTF? and Secondly, is there something I should do to check that my computer didn’t just do something dumb with the install?