Help me, i am newbie

1. yes, however you probably have both already.

2.  your x-fi is sound equipment, it has both a DAC and headphone amp in there.

3.  erm, i dont know what you mean

I think he meant how to train his listening ability to assess the sound better.

1. Yes, but a soundcard is the equivalent of DAC and amp in one. As you get sucked into this hobby you may end up getting both. A stand alone DAC has benefits of being out of the noisy environment in a computer and additional connectivity to other hifi kit.

2. I don't know enough about soundcards to say if yours is good or not.

3. The more music, headphones, hifi kit you listen to, the easier it is to pick out each ones own sound. If you are a casual listener (it accompanies you when friends are around, it is background noise during the day or when you do the cleaning), then expensive hifi is not really going to be worth it. If you intend to really listen to the music and importantly the sound of your hifi as well, then this is the hobby for you.

Welcome to Head-fi, sorry about your wallet.

1. Do you need a DAC of some kind to listen to a CD or other digital music?  Yes, but there is probably a decent integrated version in your computer/ipod/etc already.  Do you need a fancy external DAC to enjoy your (digital) music?  No.  

2. You need a signal chain to get music from a computer.  A soundcard can serve as a source, DAC, and pre-amplifier all in one.  Depending on the headphones you connect, and the soundcard itself, you may be able to get good sound by directly connecting the headphones to the soundcard (then the soundcard would be a buffer/amplifier as well).

3. Hard to answer, because you haven't defined "good listener."  Many would say a good listener is one who enjoys the music.  Others would say a good listener is a discriminating listener, able to detect small differences in audio material.  Personally, I think a good listener is one who brings beer and snacks to share with friends :) 

1. Yes and No.

Yes - you need an amplifier, and you most probably have one already.

No - a DAC is only needed for digital sources, so with an analog one (FM radio, turntable, and such) you do not need one.

2. Well, those units listed are audio equipment. So do not get the question...

3. Focused, relaxed, clean ears, ...