I found a question here to set left navigation link as default for ms crm record, while opening ms crm form.

http://social.microsoft.com/Forums/en-US/crmdevelopment/thread/9dd557d3-3828-441b-a6dc-e6c481fdb8c9

We can easily do this through JS, we just need to get ID of particular left navigation item which we can get IE Dev toolbar or Developer Tools

Paste this code on form onload event

var NavItem=document.getElementById(“Paste LeftNavigation item ID”);

if(NavItem!=null)

NavItem.click();

Done !!!