Hi mama2one,
When installing a new sheetrock wall that is going to butt up against a textured ceiling, I have found the best thing to do is to fill the crack between the wall and the ceiling with caulk and not use any tape at all. Let the caulk, and you can also use construction cement for an even better hold, hold the two panels together. If you haven't installed the sheetrock yet, you can also put 1 1/2" cross strips between the studs so that the sheetrock is very, very firm and doesn't need to be tied into the ceiling so well. Although if your home was built using basic construction techniques, you should have a solid top rail running along the top of the wall and can screw the wall sheetrock to that. Just use more screws so it's good and tight.
Personally, I don't like textured ceilings. When I move into a house that has them I generally take them down. They get dirty and are hard to paint. Especially around ceiling A/C ducts. You get a bunch of little black points where the textured ceiling catches dust coming out of the duct. It's relatively easy to take down most textured ceilings. However, it can be messy so plan on using a drop cloth and removing any furniture. Just spray the texture with plain water from a $5 hand held pump sprayer and let sit for 10 minutes. Then spray it again and take a nice sharp flat 5-6" drywall knife or scraper and just lay it nearly parallel with the ceiling and begin scraping it off. In all cases where I've done it, the texture comes off pretty easy. If it does seem hard in places or when you start, let the water set a little longer to soften up the texture. Try not to score the underlying sheetrock as you will then have to go back and fill it in, however you do usually have to refinish the tape joints anyway because a lot of times texture is put on a ceiling before it is fully taped and smoothed since the texture will hide any such problems.
God bless and let me know how it comes out.
Ted
