Get all the Teams User belongs to.

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>" +
 " <RetrieveMultiple xmlns="http://schemas.microsoft.com/crm/2007/WebServices">" +
 " <query xmlns:q1="http://schemas.microsoft.com/crm/2006/Query" xsi:type="q1:QueryExpression">" +
 " <q1:EntityName>team</q1:EntityName>" +
 " <q1:ColumnSet xsi:type="q1:ColumnSet">" +
 " <q1:Attributes>" +
 " <q1:Attribute>name</q1:Attribute>" +
 " </q1:Attributes>" +
 " </q1:ColumnSet>" +
 " <q1:Distinct>false</q1:Distinct>" +
 " <q1:LinkEntities>" +
 " <q1:LinkEntity>" +
 " <q1:LinkFromAttributeName>teamid</q1:LinkFromAttributeName>" +
 " <q1:LinkFromEntityName>team</q1:LinkFromEntityName>" +
 " <q1:LinkToEntityName>teammembership</q1:LinkToEntityName>" +
 " <q1:LinkToAttributeName>teamid</q1:LinkToAttributeName>" +
 " <q1:JoinOperator>Inner</q1:JoinOperator>" +
 " <q1:LinkCriteria>" +
 " <q1:FilterOperator>And</q1:FilterOperator>" +
 " <q1:Conditions>" +
 " <q1:Condition>" +
 " <q1:AttributeName>systemuserid</q1:AttributeName>" +
 " <q1:Operator>EqualUserId</q1:Operator>" +
 " </q1:Condition>" +
 " </q1:Conditions>" +
 " </q1:LinkCriteria>" +
 " </q1:LinkEntity>" +
 " </q1:LinkEntities>" +
 " </query>" +
 " </RetrieveMultiple>" +
 " </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/RetrieveMultiple");
xmlHttpRequest.setRequestHeader("Content-Type", "text/xml; charset=utf-8");
xmlHttpRequest.setRequestHeader("Content-Length", xml.length);
xmlHttpRequest.send(xml);
var resultXml = xmlHttpRequest.responseXML;
//alert(resultXml.xml);

// Save all entity nodes in an array.
var entityNodes = resultXml.selectNodes("//RetrieveMultipleResult/BusinessEntities/BusinessEntity");

var teamnames = new Array();
var teamids = new Array();

for (var i = 0; i < entityNodes.length; i++) {

 var entityNode = entityNodes[i];
 var teamidNode = entityNode.selectSingleNode("q1:teamid");
 var teamNode = entityNode.selectSingleNode("q1:name");
 var teamid = (teamidNode == null) ? null : teamidNode.text;
 var team = (teamNode == null) ? null : teamNode.text;

 teamnames[i] = team;
 teamids[i] = teamid;
}