Well, one would start by saying that the house is probably settling. It's not unusual to have hairline cracks, even a few of them in one wall. What you would want to do is WATCH them over time. Also, the cracks may not necessarily go all the way through the wall. If you can go outside and start looking around the area of the cracks in the basement, that might be interesting to see. The cracks may NOT necessarily line up w/the ones in the basement. THey could be offset by a foot, give or take.
Anyways, take a sheet of paper and duct-tape it to the wall. Perhaps you can take a piece of chalk and 'date' cracks in the wall and measure them. Better yet, draw them on a piece of paper and put the date and measurements there. Do note if the cracks go from bottom to top, or part-way, because over time, you'll want to know if they're growing.
If you have a New Home Warranty, I'd send a certified letter w/a Return Receipt to the Builder that expresses your concerns (if any) and what you're doing 'about' them now (tracking the cracks) and offer to set up a time for him to come out to inspect them. (ANd when he does, take special note of what he says and write it all down.) The point here is that, in a way, you're putting the Builder on notice BEFORE the Home Warranty runs out (which is usually 12 months from occupancy.) This way, if there's a problem post-12-months, you have a leg to stand on.
If you have water coming in the basement via any of the cracks, then you DEFINITELY have a problem that needs to be addressed IMMEDIATELY. If he does, take note of what measures he's taking to 'fix' the damage. From where I'm sitting, water issues related to cracks should be addressed from OUTSIDE the structure's foundation; NOT inside the house.