Sheila,

I needed something similar so I modified Jacob's SDK script a bit. You will want to replace the for loop that looks like this:

for (int i = 0; i < history.Count; ++i)
                {
                    DocumentVersion version = history[i];

                    // replace "Workflow" with your Workflow User
                    if (version.Creator == "Workflow")
                    {
                        // write an appropriate note for why this version is being deleted
                        version.Delete("This version was deleted because it was created as part of a workflow.");
                    }
                }

With something that looks like this:

for (int i = 0; i < history.Count -5; ++i)
                {
                    DocumentVersion version = history[i];

                    //Previously deleted versions have Comment = Deleted
                    if (version.Comment != "Deleted")
                    {
                        //Set Comment = Deleted and delete version
                        version.Delete("Deleted");
                    }
                }

Just make sure if you edit the delete comment to also edit it in the IF statement.