Windows 2003 comes with FrontPage 2002 extensions. There is MS FrontPage 2003 client program, but not server extensions. FrontPage 2003 client program works with FrontPage 2002 server extensions. There is no such thing as FrontPage 2003 extensions. Not yet, anyway.
SharePoint, on the other hand, has changed a great deal between the Windows 2000 version (SharePoint Team Services, aka SharePoint 2000) and the Windows 2003 version (SharePoint Services, aka SharePoint 2003).
Windows 2000 used SharePoint 2000 that were built on FrontPage 2002 extensions and utilized FrontPage 2002 extensions functionality.
SharePoint 2003 is a completely different product. It is based on .NET technology and not on FrontPage extensions. In fact, it cannot coexist with FrontPage extensions on the same web server (account).
This means that, if you install SharePoint on your Windows 2003 account, you will not be able to install FrontPage extensions.
This doesn't mean that you can't use FrontPage to connect to a Windows 2003 account with SharePoint installed. All of our initial testing, as well as the information we have from Microsoft, seems to indicate that FrontPage 2003 can be used to publish to a SharePoint 2003 web server.