verbs - What exactly is "なの" (nano)?

I asked a female Japanese friend to translate a sentence for me and it ends in "nano" which I took to be either an alternative question particle to -ne or -ka; or possibly two particles I don't know which could come together.

But just now I looked it up in wwwjdict and it tells me it's a "feminine copula". So does this mean "なの" (nano) is a synonym of "です" (desu) that only female speakers use? Assuming it's not very formal, what should I use instead as a noun?

Also does this mean it's a verb and if so what kind of conjugation or other forms does it have?

EDIT

Since this has turned out to be quite subtle and even controversial, here is my sentence:

(Original English: Why must life be so difficult?)

Japanese translation: なんで[人生]{じんせい}はそんなに[大変]{たいへん}なの？

Answer

Everyone's done a great job of answering this one, so I'm just going to add a quick answer. The なの that you're asking about is really just の. The な is only there if you use it after a noun or a na-adjective (きれい, 大変, 非常). The most common way of using this の is as a question marker.

そうなの - Is it really?

This is the same as そうなんですか but less formal.

何をしているの? What are you doing?

The same as 何をしているんですか. Or even less formally, 何してんの?

仕事は大変なの? - Is your work difficult?

More formally as 仕事は大変なんですか。

元気がないね。どうしたの？ - You don't seem well. What happened?

どうしたの is really common as a way of asking "What's wrong" or "What happened?"

You can use it to answer a question too (高いのよ！ - It is expensive), but I think the form you were asking about was the question form.

So for your question phrase, なんで人生はそんなに大変なの？, the の is making it a question (although it would be a question without the の) but also making it more emotional (in much the same was as のですか adds emotion). I think that women might use it without the な, even after a noun or na-adjective: 仕事は大変の?

Note here that you should only use this with kids or good friends, and that there's a rising intonation at the end.