Have you ever seen this message?
This product can only be installed if Windows SharePoint Services 3.0 has been installed first
When Yes – then you are properly trying to install the visual studio extensions for Windows SharePoint Service 3.0 Tools (aka VSeWSS) locally.
So what can we do to get it installed?
Well we need to make the install thinking that MOSS is installed. This can be done by changing a key in Registry.
Open regedit and create the following keys and string value
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Shared Tools\Web Server Extensions\12.0] "Sharepoint"="Installed"
Thats all! Now the installer things MOSS installed and you should be able to install WSS 3.0.
Btw. you might also want to add the core SharePoint assemblies located in C:\Program Files\Common Files\Microsoft Shared\web server extensions\12\ISAPI by using the gacutil.