Same like SPS 2003, MOSS 2007 also have 8 pre-configured web part page templates. It seems MOSS doesn't allow us to add the new one, so we need to customized the existing (make sure that you've backup them before you change it...).
The pre-configured templates were located in \12\TEMPLATE\1033\STS\DOCTEMP\SMARTPGS folder. We just need to open it with Sharepoint Designer or other web editor to customize them.
Note: In SPS 2003, we'll need to copy our customized template for each template folder, such as SPS, SPSNEWS, STS, etc to make our page template have the same look on each site.