Use of People Picker programmatically in web-parts and pages

Add

<%@ Register TagPrefix="Utilities" Namespace="Microsoft.SharePoint.Utilities" Assembly="Microsoft.SharePoint, Version=14.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" %><%@ Import Namespace="Microsoft.SharePoint" %>in the page.

 <SharePoint:PeopleEditor ID="spPeoplePickerUserName" Width="200" runat="server" SelectionSet="User"     AllowEmpty="true" MultiSelect="false" AutoPostBack="false" />



to store the data use
if (spPeoplePickerRespUser.ResolvedEntities.Count > 0)                                        {                                            PickerEntity selectedEntity = (PickerEntity)spPeoplePickerRespUser.ResolvedEntities[0];SPUser user = oWeb.EnsureUser(selectedEntity.Key);                                itemToAdd["Entered_x0020_By"] = user;                                        }


for edit mode,
spPeoplePickerUserName.CommaSeparatedAccounts = Convert.ToString(itemToUpdate["User_x0020_Name"]);

 if (spPeoplePickerUserName.ResolvedEntities.Count > 0)                        {                            PickerEntity entity = (PickerEntity)spPeoplePickerUserName.ResolvedEntities[0];                            accountName = entity.Key;                            int pos = accountName.IndexOf('\\');                            accountName = accountName.Substring(pos + 1);                            SetContactInformation(accountName);
                        }