You can provision the page in ONET.XML.
First add a web part page template to your site definition.
Then provision an instance of the page (with the web parted added) in your ONET.XML.
This stuff is described fully in Ted Pattison's book Inside Windows SharePoint Services 3.0
default.aspx
<%@ Assembly Name="Microsoft.SharePoint,Version=12.0.0.0,Culture=neutral,PublicKeyToken=71e9bce111e9429c" %> <%@ Register Tagprefix="SharePoint" Namespace="Microsoft.SharePoint.WebControls" Assembly="Microsoft.SharePoint, Version=12.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" %> <%@ Register Tagprefix="Utilities" Namespace="Microsoft.SharePoint.Utilities" Assembly="Microsoft.SharePoint, Version=12.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" %> <%@ Import Namespace="Microsoft.SharePoint" %> <%@ Register Tagprefix="WebPartPages" Namespace="Microsoft.SharePoint.WebPartPages" Assembly="Microsoft.SharePoint, Version=12.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" %>
<%@ Page language="C#" MasterPageFile="~masterurl/default.master"
Inherits="Microsoft.SharePoint.WebPartPages.WebPartPage" %>
<asp:Content ContentPlaceHolderId="PlaceHolderMain" runat="server">
<table cellspacing="0" border="0" width="100%">
<tr>
<td class="ms-pagebreadcrumb">
<asp:SiteMapPath SiteMapProvider="SPContentMapProvider" id="ContentMap" SkipLinkText="" NodeStyle-CssClass="ms-sitemapdirectional" runat="server"/>
</td>
</tr>
<tr>
<td>
<table width="100%" cellpadding=0 cellspacing=0 style="padding: 5px 10px 10px 10px;">
<tr>
<td valign="top" width="70%">
<WebPartPages:WebPartZone runat="server" FrameType="TitleBarOnly" ID="Left" Title="loc:Left" />
</td>
<td> </td>
<td valign="top" width="30%">
<WebPartPages:WebPartZone runat="server" FrameType="TitleBarOnly" ID="Right" Title="loc:Right" />
</td>
<td> </td>
</tr>
</table>
</td>
</tr>
</table>
</asp:Content>
<asp:Content ID="Content1" ContentPlaceHolderId="PlaceHolderPageTitle" runat="server">
<SharePoint:ProjectProperty ID="ProjectProperty1" Property="Title" runat="server"/>
</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderId="PlaceHolderPageTitleInTitleArea" runat="server">
<label class="ms-hidden"><SharePoint:ProjectProperty ID="ProjectProperty2" Property="Title" runat="server"/></label>
</asp:Content>
ONET.xml snippet
<Module Name="Default" Url="" >
<File Url="default.aspx" Type="Ghostable">
<!-- Add a Web Part to left zone -->
<AllUsersWebPart WebPartZoneID="Left" WebPartOrder="0">
<![CDATA[
<WebPart
xmlns="http://schemas.microsoft.com/WebPart/v2"
xmlns:cewp="http://schemas.microsoft.com/WebPart/v2/ContentEditor">
<Assembly>Microsoft.SharePoint, Version=12.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c</Assembly>
<TypeName>Microsoft.SharePoint.WebPartPages.ContentEditorWebPart</TypeName>
<Title>Working with Site Definitions</Title>
<FrameType>TitleBarOnly</FrameType>
<cewp:Content>
This Web Part was added through declarative logic in ONET.XML
</cewp:Content>
</WebPart>
]]>
</AllUsersWebPart>
</File>
</Module>