Forum Moderators: phranque
I don't know if there's an equivalent capability with IIS, but if there is it's a good alternative because the page names stay exactly the same, just with the added ease and functionality of using SSI. If not, you may want to consider a move to Apache if it'll make your life simpler long term.
Oh, and welcome to WebmasterWorld!
The solution to your problem is FP's Included Content (That's what it's called in FP 2003. In earlier versions it was Include Page.) The Include works just like SSI, but will only work between your <body> tags. It is very powerful and will save you from FP's Shared Borders which are the cause of many problems.