This has been requested in the past: shtml usually means you have true "server side includes" working on that page. In fact the ssi-mod is named inacurately, as it isn't using the server side includes technology, but plain php includes. When I started ssi-mod I had in mind to make it work for true ssi as well, but I failed (one reason for this being the fact that I didn't have access to a webserver that had ssi at that time), so I gave up. Basic answer is: in theory, it is possible, but it requires someone with know-how to look into this. I won't be that one, as I have abandoned this mod a long time ago, sorry. Currently, the mod will not work on ssi-enabled pages, so the short answer to your question is: the mod will not work for shtml pages.
Joachim
Actually, I have got it to work quite simply in shtml, with a quick little hack.
I created a php file 'random.php' which is simply
<?PHP
include_once("path/to/ssi.php");
print cpg_random();
?>
Then in my shtml page, I simply have
<!--#INCLUDE VIRTUAL="random.php" -->
Works a charm! (website is
www.wnt.org.au, the random photo is in the top right hand corner using this method)
Right now I'm trying to implement another random (album specific) ssi on the same page, so if you load it and it looks wierd, that's why!
Oh, and the other way to do it (if your server supports it) is to make the page php and use the php functions virtual() (instead of <--#INCLUDE VIRTUAL--> and include(). My server had issues with virtual() (they claimed it should work, but it didn't), so I did this.