Well, if your EntryBody is where you're placing the photos, then your template for your include would be
CODE
<MTEntries lastn="4">
<MTEntryBody>
</MTEntries>
And you would include that using PHP:
CODE
<? include '/path/to/file/lastfourentries.php' ?>
You could do the same thing with the Excerpt field if that's where you're placing your thumbnails.
Re: making thumbnails - I think you're going to have to do that either through MT, or upload the photo twice, once at one size, and once with a "photo-thumb" name in a smaller size - I've never moblogged, so perhaps your Treo user manual might have thumbnailing suggestions?
Does this help?
Donna