PROPER setups will only replace DLLs with NEWER versions. The embedded version numbering/date resource fields are checked. A setup should NEVER EVER replace a DLL with an older one. Anyone distributing such a monster should be hung from the thumbs until dead.
Some setups are courteous and ASK whether to substitute the newer version. Might mean a few extra clicks now and then but it will let one protect that all-to-fragile Windows 98.
BTW, I have had too many fatal problems with InstallShield distributions. I have never crashed from WinZip self-installers or Wize setups. This, I hope, with all its implications, is self-explanatory.
