When you build a custom portal provisioning script, you have to uniquely identify your template for WSS. Many times I see that people are working with numeric IDs and the guideline is that you start from 10000 to identify your own custom templates. But there is no guarantee that the number you assign here will ultimately be unique on the front-end Web Servers since other developers can create definitions also or maybe you are installing templates you download from the community or from 3rd parties.
It is better to just assign a GUID as the value for the ID attribute in the XML. This will make sure your portal template is going to be unique wherever you deploy it.
<Templates xmlns:ows="Microsoft SharePoint">
<Template Name="U2UPortal" ID="{88F4E732-4F7C-48ab-9E5A-1DFD4A69751E}">
<Configuration ID="0" Title="U2U Portal Kit" Hidden="FALSE"
ImageUrl="/_layouts/1033/images/IPPTU2U.gif"
Description="This template can be used to create a starter internet site for U2U."
ProvisionAssembly="Microsoft.SharePoint.Publishing, Version=12.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c"
ProvisionClass="Microsoft.SharePoint.Publishing.PortalProvisioningProvider"
ProvisionData="xml\\u2umanifest.xml"
RootWebOnly="TRUE" DisplayCategory="Publishing"
VisibilityFeatureDependency="97A2485F-EF4B-401F-9167-FA4FE177C6F6">
</Configuration>
</Template>
</Templates>