A search of google reveed that only a plesk installaiotn can read that file. So you're best bet would be to upload your plesk file to the server, and import it back into your account, and then do a traditional dump of the database and your files.
If that's not going to work for you, I'd sigguest you pay for a month's hosting at an other host that uses plesk, and do that same as above, BUT - beware. There may be versioning issues with your backup file. You'll want to find a temporary host that is running the same version that your backup was created with.