is it personal site or business? if it's for business I definately would not, you don't know the type of copyright they have on it and you don't want to get in trouble. Especially if you don't take out all the correct coding and both sites come up in a google search.
If it's for personal use I really wouldn't be as concerned, although it's better if you go onto a site with templates instead of stealing someone elses idea. I'd also give them credit in the code.
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