Sofaspud is correct. Also, Bob, the code you are having the server insert has nothing but the section of code needed, no doctype, header information, etc.
When I've used it in the past I've used .htmlf as the extension letting me know that it is an html fragment not a full webpage. The way SSI works, at
least under Apache, I've not used IIS, is that the site administrator tells Apache what extension(s) to look for to know when to scan. Normally, most
sites use .sht and .shtml tell the server to scan the webpage before sending it and to look in the page for the #include "command". If one is found
then it will insert the file listed in the link as if it were typed in from the beginning. If you name the original file something other than the selected
extension(s) the server will not scan the file and nothing will be included. (With Apache you could use the XBitHack, if turned on, to not have to rename all
your pages but you'd have to have chmod access to the files to set the x bit.)
One caveat, make sure that the server is powerful enough to handle the load as the file has to be scanned and manipulated for each connection. As you appear
to be using a hosting site that should not be a problem. With that said, SSI is very powerful. At work we use it to generate the whole main page. Everything
is made up of .htmlf files loaded around the "wrapper" main page. That way we can change the layout without worrying about the information being
lost during a change. The information just "flows" into the new layout so no cutting and pasting from one file to another when making major layout
changes.
Edit -- Fixed typos and made thoughts clearer.
When I've used it in the past I've used .htmlf as the extension letting me know that it is an html fragment not a full webpage. The way SSI works, at
least under Apache, I've not used IIS, is that the site administrator tells Apache what extension(s) to look for to know when to scan. Normally, most
sites use .sht and .shtml tell the server to scan the webpage before sending it and to look in the page for the #include "command". If one is found
then it will insert the file listed in the link as if it were typed in from the beginning. If you name the original file something other than the selected
extension(s) the server will not scan the file and nothing will be included. (With Apache you could use the XBitHack, if turned on, to not have to rename all
your pages but you'd have to have chmod access to the files to set the x bit.)
One caveat, make sure that the server is powerful enough to handle the load as the file has to be scanned and manipulated for each connection. As you appear
to be using a hosting site that should not be a problem. With that said, SSI is very powerful. At work we use it to generate the whole main page. Everything
is made up of .htmlf files loaded around the "wrapper" main page. That way we can change the layout without worrying about the information being
lost during a change. The information just "flows" into the new layout so no cutting and pasting from one file to another when making major layout
changes.
Edit -- Fixed typos and made thoughts clearer.