Hantang House is located in a small alley (Nanchang Xiang) that you can easily overlook. Even after I got to the hostel and saw the alley, when I tried to find it the other day, after taking a trip around the city, I couldn't remember where it was. So I'm adding a photo of the entrance to the alley, so you can memorize it. You can also take the Shaanxi People's Government as a landmark - the Nanchang Xiang Alley is located southern to it, just a few minutes' walk.
I arranged a pick-up from the airport to the hostel (but had to ask them again and again that they will really pick me up, because their reply wasn't very clear) which cost me 150 yuan. It was a good choice to take the pick up, because my flight got delayed 4 hours and I arrived in Xi'an at 1 in the morning. I was worried that the pick-up won't wait for me that long, but I was happy to see that they waited for me.
The hostel itself looks very modern. The room is very clean, but I had a feeling that the heating wasn't that good. Music is playing in the first floor and bar all day long, which is nice. The staff were all very nice, smiled and were willing to listen and spoke English well. The food that they serve is mostly Western (and so is more expensive). I could find only around 4 types of Chinese food in the snacks menu. The tours that they offer look great and their prices aren't very high. Overall it was a nice stay.
Chinese address for taxi: 西安市新城广场南新街南长巷32号 (I would recommend you to print out important addresses before you arrive in China, because it really helps)