Impersonation

//createdby     - user 1
//owner         - user 2
//impersonate   - crm-service
CrmAuthenticationToken token = new CrmAuthenticationToken();
token.AuthenticationType = 0; // Use Active Directory authentication.
token.OrganizationName = "LP";

// Use the global user ID of the system user that is to be impersonated.
token.CallerId = new Guid("C0C0A8E9-A72D-E011-80B9-00155DC85005"); //user 1

CrmService crmService = new CrmService();
crmService.Url = "http://tl:5555/MSCRMServices/2007/CrmService.asmx";
crmService.CrmAuthenticationTokenValue = token;
crmService.Credentials = new System.Net.NetworkCredential("CRM-Service", "Password2k", "company");

// Create a new account owned by the impersonated user.
account account = new account();
account.name = "Fabrikam !!";
Owner owner = new Owner();
owner.Value = new Guid("D57CC3F3-A92D-E011-80B9-00155DC85005"); //user 2
owner.type = EntityName.systemuser.ToString();
account.ownerid = owner;
Guid accountid = crmService.Create(account);