You might want to read this thread: Server upgrade problem
Since all versions of filemaker from filemaker 7 to 11 use the same data format in their files. Server 9 will be able to host the files. There may be some new features of filemaker 10 & 11 that aren't available to you if they depend on server side processing. You can down load a trial version of filemaker 11 and use it as your client on this network to test things out.