DLL's do not live in the registry. The are found either in C:\Windows; C:\Windows\System or the program's own folder. The registry contains the necessary info to run them. Dll's sometimes need to be registered, if that is what you mean. To do this you use the register server (regsvr32.exe) but for a program from the days of win3.11 I don't think it will work.
To use it, assuming you are using XP: Start\Run and type C:\Windows\System32\regsvr32.exe leave a single space and type the full path and name of your dll. If you works you will informed.