You might well already be aware of this, but just in case: exporting XML from Excel will not result in anything like an importable document for OCS. (The two formats have as much in common as English and Cantonese; "XML" is tantamount to both of them being spoken languages). A conversion process is something that would require quite a bit of effort.
The DTD describes the format OCS expects, and comes with the OCS installation. (It's also available for download at http://pkp.sfu.ca/ocs/dtds/native.dtd
). You'll need someone sufficiently familiar with XML that they can read this.
OCS accepts XML documents that include paths to submission files (e.g. presentations or word processor documents), so typically what you'd do is include the paths in your import XML and when OCS ingests the file it'll also take in the submission files it refers to. Of course, you could add these manually afterward as an alternative.
Public Knowledge Project Team