>Does anyone knows what regsrv32.exe that came vith VFP5 is it for?

It's a tool for registering and unregistering ActiveX Controls and in-process OLE Servers.

>When do I need to use it?

It should be used when adding or removing COM components on a system by hand, and may be used by various installers to handle the registration tasks that they require performed. It's also used when some shared components that aren't really OLE Servers, but that use the common server registration entrypoint to maintain information about themselves in the registry, are updated or added to a system.