We have a 12 week old jack russell. She does fine in her crate if we are in the room. When I leave the house and crate her she cries hysterically, howls and vomits every time. The howling and crying never stops. It doesn't matter if I am gone 30 minutes or 2 hours. While we are home she wonders in and out of the crate at will. When leaving her we always give her something to play with and a treat. I need help. I have to leave the house and can't leave her running loose.

Hmmm, separation anxiety. Tricky but not incurable. Have you by chance had her for a number of weeks now? Sometimes if they are separated from their mother too soon, anxiety will arise when left alone. You may try gradual separation, which basically means weaning her off the idea of you being around all the time. Start with going outside for a short time with her shut in the crate, depending on how long it takes for her to get agitated. Seconds, minutes maybe. Try and time it so that you come back inside before she starts getting anxious but don't give her any praise or attention when she sees you. Then simply go back outside again and repeat the process until (hopefully) she can hold out for at least an hour or so without getting agitated. By this stage it should be OK to leave for as long as you need to. The other thing you could try is to put a radio or TV on while you're out.
BTW does she sleep in the crate at night?
Hope this helps.:)

When we got her she was 10 weeks old. We have had her for 2 weeks today. I always leave the stereo on. At first we crated her at night, after 4 nights of screaming and howling the entire night, we started letting her sleep with our 16 year old. Not a peep al night long, hasn't had an accident in his room yet. During the day we are down to maybe 1 accident in the house every other day. I have been crating dogs for 20 years and have never had one not adjust to it after the first day.

I agree it is most likely separation anxiety. You say he can go in and out of his cage when you are home but evidently you shut him in when you go out. Try closing the cage when you are home to see if he still cries.
I hate caging dogs so I block mine in a non carpeted room (usually the kitchen or my enclosed back porch) when I need to leave for awhile.

My dog used to cry a lot when I first got her... almost sounded like a seal. I immediately gave her one of my t-shirts (that I wore to go running in) and she stopped crying almost within a day or two.

I will try a piece of clothing. The crying and howling does create a problem, with the windows open the neighbors can hear her. My real concern is she is so upset she vomits every time, and its projectile vomiting. I appreciate the feed back I have received so far.
Thanks

You could try, if you aren't already using one, a metal crate that she can see through all parts of. Sometimes the anxiety occurs when you are simply out of sight, around the corner. Play peek a boo, showing her that you will always become visible again. She is afraid that you will never reappear. Human babies sometimes go through a phase of this. They don't have enough life experience to know that if they can't see mom, she still exists.

It is metal. We have tried 2 different sizes. One that is her size, then we tried a larger one our doberman used and put a travel soft sided carrier inside of that. The larger one worked the first day then it was back to the vomiting again. Thanks for the imput.