How to set up OpenSearch in Drupal?
From looking at these three modules closer, I see that only the opensearch module has a 7.x branch: https://drupal.org/node/74142/release.  You could try using that branch, but it probably not ready for a production system.  

It looks like Kiam is the module author you may be able to contact him to find out if he is planning to complete the Drupal 7 version.