I gather that iWeb08 now provides some sort of expert/raw HTML editing mode/setting that the earlier versions of iWeb did not, so if this is accurate, it may now be possible to integrate our code into an iWeb site by using iWeb entirely and without resorting to re-editing your page in another program.
I haven't dealt with an iWeb-maintained site in a while, but IIRC, I think only the View Cart code needs to be manually pasted-in to avoid iWeb's IFRAME problem with our cart. Offhand, I can't remember if this is because iWeb only puts code snippets into an IFRAME if they have raw JavaScript in them (which View Cart does and Add to Cart does not), or if it actually IFRAMEs all code snippets but that only causes a problem with the View Cart code, but the upshot is the same -- View Cart code cannot work as an IFRAME'd code snippet and must go directly into the raw source of the page itself.