/* the function */
ExecuteWorkflow = function(entityId, workflowId)
{
     var xml = "" + 
     "<?xml version=\"1.0\" encoding=\"utf-8\"?>" + 
     "<soap:Envelope xmlns:soap=\"http://schemas.xmlsoap.org/soap/envelope/\" xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\" xmlns:xsd=\"http://www.w3.org/2001/XMLSchema\">" + 
     GenerateAuthenticationHeader() +
     "  <soap:Body>" + 
     "    <Execute xmlns=\"http://schemas.microsoft.com/crm/2007/WebServices\">" + 
     "      <Request xsi:type=\"ExecuteWorkflowRequest\">" + 
     "        <EntityId>" + entityId + "</EntityId>" + 
     "        <WorkflowId>" + workflowId + "</WorkflowId>" + 
     "      </Request>" + 
     "    </Execute>" + 
     "  </soap:Body>" + 
     "</soap:Envelope>" + 
     "";  

     var xmlHttpRequest = new ActiveXObject("Msxml2.XMLHTTP");
     xmlHttpRequest.Open("POST", "/mscrmservices/2007/CrmService.asmx", false);
     xmlHttpRequest.setRequestHeader("SOAPAction","http://schemas.microsoft.com/crm/2007/WebServices/Execute");
     xmlHttpRequest.setRequestHeader("Content-Type", "text/xml; charset=utf-8");
     xmlHttpRequest.setRequestHeader("Content-Length", xml.length);
     xmlHttpRequest.send(xml);
     var resultXml = xmlHttpRequest.responseXML;
     return(resultXml.xml);
} 

/* call */ 

var theWorkflowId = "3FD2DD58-4708-43D7-A21B-F0F90A0AA9F2";
//change to your workflow Id 

ExecuteWorkflow(crmForm.ObjectId, theWorkflowId);