Bring a large pot of water to a boil. Cook pasta according to package directions. Drain, reserving 1/2 cup of pasta water. Set aside.
Meanwhile, in a large skillet, cook ground beef and chopped onion over medium-high heat. Cook until the beef is no longer pink. (Drain any grease) Then add minced garlic, cook and stir for 30 seconds. Stir in the can of diced tomatoes and taco seasoning. Let simmer over medium heat for about 5 minutes.
Stir in cooked pasta, cream cheese, sour cream, and 1/2 cup pasta water. Cook and stir until the cream cheese has melted and the sauce is well blended. Season with salt and pepper to taste. Simmer over low heat for another 5 minutes, or until the sauce has reduced a bit. Serve!