I have installed CRM 2011 beta and liked it very much with the new enhancements and features.
dying to see it realeased in January 20th, 2011
enjoy ;)

// this code is to get the number of activities and historical activities.
var buXml = GetRegardingActivity();
if(buXml != null)
{
var buNodes = buXml.selectNodes("//BusinessEntity/q1:statecode"); // CRM 4.0
var iActivity = 0;
var iHistory = 0;
if(buNodes != null )
{
/*get values*/
for( i = 0; i < buNodes.length; i++)
{
switch(buNodes[i].text)
{
case "Open" : iActivity++; break;
case "Scheduled" : iActivity++; break;
case "Completed" : iHistory++; break;
case "Canceled" : iHistory++; break;
}
}
if(document.getElementById('navActivities') != null)
{
document.getElementById('navActivities').getElementsByTagName('NOBR')[0].innerText = document.getElementById('navActivities').getElementsByTagName('NOBR')[0].innerText + " (" + iActivity + ")";
}
if(document.getElementById('navActivityHistory') != null)
{
document.getElementById('navActivityHistory').getElementsByTagName('NOBR')[0].innerText = document.getElementById('navActivityHistory').getElementsByTagName('NOBR')[0].innerText + " (" + iHistory + ")";
}
}
}
function GetRegardingActivity()
{
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>activitypointer</q1:EntityName>" +
" <q1:ColumnSet xsi:type="q1:ColumnSet">" +
" <q1:Attributes>" +
" <q1:Attribute>statecode</q1:Attribute>" +
" </q1:Attributes>" +
" </q1:ColumnSet>" +
" <q1:Distinct>false</q1:Distinct>" +
" <q1:Criteria>" +
" <q1:FilterOperator>And</q1:FilterOperator>" +
" <q1:Conditions>" +
" <q1:Condition>" +
" <q1:AttributeName>regardingobjectid</q1:AttributeName>" +
" <q1:Operator>Equal</q1:Operator>" +
" <q1:Values>" +
" <q1:Value xsi:type="xsd:string">" + crmForm.ObjectId + "</q1:Value>" +
" </q1:Values>" +
" </q1:Condition>" +
" </q1:Conditions>" +
" </q1:Criteria>" +
" </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;
return resultXml;
}
Source: http://mscrmblog.net/2009/05/18/show-no-of-open-closed-activities-history-on-the-crm-form/