Filemaker 7 and Filemaker 11 files use exactly the same format. Even the .FP7 at the end of the filenames has not changed.
You should be able to simply open your original files with FMP 11 and start using them.
Any chance there's a platform change from mac to windows going on here?
Did you create the files without .fp7 on a Mac and now you are using a windows machine to find and open them?
If so, edit the file names by adding .fp7 to the end of them and then you can use FMP 11 to find and open them.