You will notice that in the 2007 documentation we moved to the phrase of reverse proxy when discussing the publishing of content, but obviously if we document any product it will be ISA. We never state you can't use another product, it is just that we don't test or document any of the competing products.
Chris forwarded his work and I hope it helps you -
November 5 edit - In my haste I failed to mention that we didn't test the product in the topology that Chris mentions which means it would not be officially supported.
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