If you JUST received it and it's going brown, it's likely the damage was done long before the symptoms became evident. What you described doesn't bode well for your juniper. Your best bet would probably be to depot it and put it in the ground until spring, at which time you can lift it and pot it in an appropriate soil - same pot it's in or another of your choosing. I know it's a tough call, but it doesn't sound like the probability of survival is on your side.

Al

Tapla - I've had it for a month or so before the browning started.

OC - I've held off watering it since the soil is still wet, I'll keep going until it's drier. Problem is, the needles all over the plant are drying out and falling off. Am I already too late?

Where do you keep it? Junipers need to stay outdoors 24/7/365.

Why don't you return it and get a better tree???
It's possible it was dead (but still green) when your in-laws bought it. They have been known to look alive for a long time after dieing (the trees not the in-laws).