I have built a new interior wall in a room that had existing textured ceilings. I'm just wondering how to go about mudding the seams where the new wall meets the old ceiling. I assume I'll want to scrape the texture off so that the tape can lay flat against the ceiling? I've never done texturing so if there is a way to get by without having to ruin the existing texture that would be preferable.

The cheat for this situation is to run a bead of Silicon Latex caulk at the junction instead of tape and mud. This is a far from optimum solution. It all depends on where your quality craftsmanship threshold rests. At the perfect end of the spectrum you will be redoing your entire ceiling.

I have new drywall and I have taped and mudded. However, every time I put the mud on, I continually get bubbles. This only happens in an area of 5 feet by 2 feet. All other areas and walls do not bubble. I have tried both types of mud (pre-mixed, and mix myself). Any suggestions and/or reasons I am getting bubbles in just one area?
Kali

Check the surface of that area. You will probably find many little craters. When you apply the mud you cover but don't fill those holes. As you work the mud, the air in the crater is compressed and when your knife moves past, the air push out the mud. Try thinning out your mud a little more.