Xiaodong,
If you have a stub .dll that calls your main .prg that's marked external in your project, then you can simply replace the main .prg on the web site without stop/starting anything.
Alternatively, if you place your VFP .dll in a Virtual directory on your web server, you can simply press the 'Unload' in the IIS console if the application is running in high or medium isolation mode.
For development, you can even automate the Unloading of the Virtual directory with the following code in a project hook:

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

>I am going to put up a web service .DLL on our website.
>Question is, we are on a shared hosting environment. Do we have to re-start the server everytime I upload a newer version .DLL? What needs to be re-started? HTTP server? IIS?
>
>~Sheldon