Actually there is a pretty good explanation of "nante" at http://www.nafai.org/japanese/grammar/nafjpphrases/ section 12.3 "The many meanings of 'nante'" (even though it's listed in the TOC as 12.2). In particular, when used at the beginning of an expression, "nante" means "how/what", as in "how lovely!". so "nante kirei na" means "how pretty!" (actually, the -na here is not the one used with na-type adjectives but rather the exclamation -naa, like -yo or -ne). "nante majime na gakusei deshou" means "what a diligent student!" and so on. "nante" is used quite often in both spoken and written japanese language, so it's important to be able to interpret it naturally without disrupting the flow of the sentence.

Hope this helps.