Let me tell you something that will probably make you feel alot better. After 2 out of 3 of my cats died, my last cat seemed a little lonely. So I thought I'd get her a little kitten friend and she'd be happy - WRONG! Sadie attacked the new kitten, wouldn't stay in the house for 5 minutes, attacked us, and tore up the furniture! Well, this little kitten, Misty, was so sweet we just couldn't get rid of her so we thought "Fine! If Sadie's gonna be like that, she can just become an out door cat like she wants."
After about a month, Sadie started coming around more because we kept the kitten strictly in one room. After introducing them like everyone told me over and over and over and over.....it finally paid off. Misty and Sadie can now be in the same room together, as long as Misty doesn't get too close to Sadie. Although, today they touched noses twice, and Sadie let Misty sit about a foot away from her was bathing herself! Amazing progress from when we first got Misty! Sadie even lets us get around her more, and she's never been real friendly ever since she was a kitten herself.
So just hang in there, and I promise they'll learn to co-exsist - at least!