DLL registration directory?

During installation of your application, is it the norm to copy your dll to a specific directory (like C:\Windows\System???) and register it there...or do people typically just copy the dll into your "application directory" (like C:\Program Files\myapp) and register it there? Thanks in advance!!

Use Package & Deployment Wizard or InnoSetup www.innosetup.com to Deploy your Program. Include the DLL's and it will register for you itself.

Use Package & Deployment Wizard or InnoSetup www.innosetup.com to Deploy your Program. Include the DLL's and it will register for you itself.
So, those products will select the directory to copy the DLL to? Or, do I still need to select that?

ActiveX components (DLL/OCX/EXE) that could be shared system wide
should be in a shared or system folder. Ones that are specific to the the
app and would never be used by another one should be in a folder
related to the app. Standard DLLs specific to the app need to be in the
app's folder.