Why not update from 10.5.0 to 10.5.8?

Hard Drive crashed and inserted retail CD disk and ran utility indicated was not repairable. I tried repartitioned (journaled), ran verify and repair and indicated that the volume was ok. It Installed retail 10.5.0 properly. It then downloaded combined update of 10.5.8 but would not install indication that it could not install on the volume. I assume the HD is still bad or there is a software issue. I believe this is the same software CD I installed earlier on this machine. Any ideas?