Sheldon,
Place your vb .dll in a virtual directory under IIS and run the Virtual Directory in High or Medium isolation (these options are visible if you right click the virtual directory and select properties from the IIS console). After that, when you want to replace it, simply press the Unload button in your Virtual Directory Properties - no need to Stop/Start IIS.
This could be automated in a .exe or .dll using the following ADSI code:

DirObj=GetObject("IIS://LocalHost/W3SVC/1/Root/"+myVirtualDir)
DirObj.AppUnload

>Hi,
>
>We are developing a web site hosted in a shared environment and using some Visual Basic dlls. Whenever we need to make change, we have to do following,
>in vadmin,
>(1)unregister the old dll,
>(2)stop the server,
>(3)WAIT 24 HOURS OR EVEN LONGER so that
>(4)we can upload and register the updated dll.
>
>This sounds rediculus. We have to WAIT otherwise not able to overwrite the old dll.
>
>We must do know how to do it correctly. please help...
>
>~Sheldon