The Hebrew writing system doesn't have very much in common with the English one. There isn't a "right" or "wrong" way to write it in the English alphabet, because it is not an English name. It is a Hebrew name and written in Hebrew letters. It's not pronounced in English like it is in Hebrew, so it has no reason to be spelled the exact same way (And we don't even have the same letters, so it can't be spelled the same way).
The only consideration when transcripting names is tradition - traditionally the letter heh can be translated to "H", as in Sarah, Dinah, etc., so it's certainly "legit" to transcript ðåòä as Noah. OTOH you have Rebecca and Jemima, for instance, in which an H is traditionally not added. It's all down to personal preference in this case - and since Noah is a pretty common name for a boy, I prefer to spell my name as Noa (when I ever need to write it in English) so that it's clear I'm a girl, and the H is unnecessary IMO.
This message was edited by the author on April 19, 2009 at 1:29 PM