Generally, when archiving, having an archiving strategy in place is critical. For example for my current client, we use a record centre and have retention policies that move the form but leave a link in the list. This way the file cannot be edited, since it is a record. But the documents remain in SharePoint itself.
If you are happy for the InfoPath forms to live in a archival site collection, then you can create a workflow (either SP designer, Custom or Nintex) and move the file to the relevant archival site collection based on created date.
Now if you are looking for moving the InfoPath forms to a file system, then you will need to use SharePoint object model and write some C#/ powershell code to get the first 100 documents and place them on the file system where they will be backed up. And you can schedule a job on the server so the code runs every day (or as per your schedule) but with this approach there will be no links to these files
How to read list items e.g. http://msdn.microsoft.com/en-us/library/ms456030.aspx
Sorry the question was a bit vague so tried to include as much as possible.
Hope it helps.