It is not possible to directly "embed" a Tumblr or WordPress blog into your SupaDupa boutique, as neither of those services support framed embed options, and their is no option on SupaDupa to support embedding in such a manner either.
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What you may be referring to by the word "embed" is having a blog on another service and making them look the same. An example of this is a SupaDupa user AnyForty, who has their SupaDupa shop at http://www.anyforty.com and their Tumblr Blog at http://blog.anyforty.com
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It is important to note that in the example case above, the blog is NOT embedded, but remains hosted on Tumblr. The "blog" sub-domain has been pointed to Tumblr to add cohesion to the brand, neither of which have anything to do with SupaDupa.
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The reason they look the same is that in this case AnyForty had hired someone to customise the HTML & CSS of their TUMBLR blog to appear similar to their SupaDupa boutique.
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