A server side include is something used to, amoung other things, include one page within another - much like the frontpage 'Include Page' function but using different code.The code for using a server side include would be something like:
<!--#include virtual="/directoryname/filename.htm"-->
SSI - or serverside includes - have nothing at all to do with FP server extensions and are supported by the vast majority of hosts.
ASP or active server pages are cretaed using a database and must be on a Windows NT server to function.
If you were previously using FP includes then as far as I understand these do not need server extensions to function but if they are giving problems look at the possibility of using SSIs instead - the effect is identical.
If your host does not allow you to use even SSI then I would high-tail it out of there and move somewhere else. 
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Katherine
InKK Design
LinKKs - Kilkenny's Online Magazine
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