Setting a user lookup with the current user with Javascript in MS CRM 2011

If you want to get current user id in MS CRM 2011 form you can use following script: Xrm.Page.context.getUserId()

For setting  a user lookup for logged in user use following script
function SetUserInfo() {
 var context;
 var serverUrl;
 var UserID;
 var ODataPath;
 context = Xrm.Page.context;
 serverUrl = context.getServerUrl();
 UserID = context.getUserId();
 ODataPath = serverUrl + "/XRMServices/2011/OrganizationData.svc";
 var retrieveUserReq = new XMLHttpRequest();
 retrieveUserReq.open("GET", ODataPath + "/SystemUserSet(guid'" + UserID + "')", true);
 retrieveUserReq.setRequestHeader("Accept", "application/json");
 retrieveUserReq.setRequestHeader("Content-Type", "application/json; charset=utf-8");
 retrieveUserReq.onreadystatechange = function () {
 retrieveUserReqCallBack(this);
 };
 retrieveUserReq.send();

}

function retrieveUserReqCallBack(retrieveUserReq) {
if (retrieveUserReq.readyState == 4 /* complete */) {

if (retrieveUserReq.status == 200) {
 var retrievedUser = this.parent.JSON.parse(retrieveUserReq.responseText).d;
 if (retrievedUser.FullName != null)

var setUservalue = new Array();
 setUservalue[0] = new Object();
 setUservalue[0].id = Xrm.Page.context.getUserId();
 setUservalue[0].entityType = 'systemuser';
 setUservalue[0].name = retrievedUser.FullName;

Xrm.Page.getAttribute("from").setValue(setUservalue)
 }

else {

 }
 }
}