Hi,
To create a case record from c# refer: http://ekoncis.blogspot.in/2012/01/crm-2011-create-new-case-incident-using.html
Entity incident = new Entity("incident");
incident["title"] = "Case subject";
// Set customerid with some existing contact guid
Guid customerid = new Guid("{xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}");
// Set customerid as contact to field "customerid"
EntityReference CustomerId = new EntityReference("contact", customerid);
incident["customerid"] = CustomerId;
// Set contactid with some existing contact guid
Guid contactid = new Guid("{xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}");
// Set contactid as contact to field "casecontactid"
EntityReference primaryContactId = new EntityReference("contact", contactid);
incident["casecontactid"] = primaryContactId;
_service.Create(incident);