I'm not sure what the postflight is on 10.5.7. It might not hurt to run the combo update just to be safe, but my guess is if you booted at all, you're probably fine. Normally, the postflight just executes commands to hide hidden files like /mach_kernel and stuff. In terms of importance, it usually ranks somewhere around 2 on a scale of one to ten. That said, I can't guarantee that this one doesn't do something more important. Probably not, but I can't guarantee it without reading through the script.
I'll try to remember to have a look at the script tomorrow. If anything in the postflight jumps out at me, I'll follow up in this thread. If you don't hear anything from me in the next day or so, roll your eyes and don't worry about it. If it concerns you though, just install the combo update (or probably even the standard update) and it should succeed.
