There is a property called UserInfo on the base class your module should be inherting.(DotNetNuke.Entities.Modules.PortalModuleBase). UserInfo has the details your after. So you could use (this|me).UserInfo.UserID, or if you don't need the extra details involved in the UserInfo object you could also use (this|me).UserId as well.
Forgive the C# below, if you need a vb version and C# is totally off the wall to you let me know and I will list that as well. Anyway, To load a userinfo up from an ID you have or have stored stored somewhere like the db =), you can get the details of them like so...
DotNetNuke.Entities.Users.UserController oUserController =
new DotNetNuke.Entities.Users.UserController();
DotNetNuke.Entities.Users.UserInfo oUserInfo = oUserController.GetUser(
this.PortalId, iSomeUserID);
oUserController =
null;
//Set Some Label or textbox.Text of the username
txtSomeTxtBox.Text = oUserInfo.Username;
//Etc.
HTH's,
Dave