How to access 'name' given when user registers

[xnaLearner]

So I only want the logged in user to be allowed to book holidays for them selves. I think the easiest way to do this is to compare 'name' of logged in user againast 'name' in person table. So....

public ActionResult Create()
{
string xx = (string)Session["usernameID"];
int? currentPersonID = Convert.ToInt32(xx);

        string userNameComparedAgainstLoginName = // here is where i want to say 'name' of logged in user

        CreateModel model = new CreateModel();
        model.currentPersonID = currentPersonID.Value;
        model.PList4DD = db.People.ToList();   
       

        if (userNameComparedAgainstLoginName == model.userName)
        {
            ViewBag.Id = new SelectList(db.People, "Id", "Name");
            return View(model);
        }
        else
        {
            TempData\["canOnlyBookHolidaysForYourself"\] = "I'm afraid you can only book holidays for yourself";
            return RedirectToAction("Index");
        }
    } 

--------------------------------------- the name given when the user registers will be the same names used in the db. So could someone tell me how I can access the logged in 'name'? Thanks

[xnaLearner]

forgot to mention Its just the automatic login that comes with mvc3 razor