If you can not re-apply a HOTFIX because the system reports it is already installed, and you can't remove it via HOTFIX /remove, edit:
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\HOTFIX and delete the Hotfix entry.
Then use Explorer to navigate to %windir%\HOTFIX\Hf00... or after NT 4.0 SP3, the %windir%\$NtUninstallQ.....$ and delete the HOTFIX entry. Reboot and re-apply the HOTFIX. If you know that you will be re-applying a Service Pack, try removing the HOTFIX first.