and I'm surprised that Heartinternet don't run the FrontPage 2002 extensions, which are compatible with FP 2003.
Microsoft is discontinuing FrontPage now - there'll be no further versions of it. The successor is a program called 'Expression Web Designer', which is based on Frontpage, but has greater capabilities. It's in the beta stage at the moment, but it's very good, and you can download a free trial (of the beta1 version) if you click here
I know that doesn't help you with your FP problem, but I can't suggest anything for that, other than revising your site so it doesn't use any of the special FP components like animated buttons etc. If you do that it will run perfectly.