Fire up Windows PowerShell et run:
$strSID="S-1-5-21-500000003-1000000000-1000000003-1001"
$uSid = [ADSI]"LDAP://<SID=$strSID>"
echo $uSid
The output should look something like this,
distinguishedName : {CN=John Doe,OU=Domain Admins,OU=People,OU=xxx,DC=xxx}
Path : LDAP://<SID=S-1-5-21-500000003-1000000000-1000000003-1001>