There is LOTS of info on the WEB on How To Paint. And there are books too. The fact that you have heating ducts coming through the ceiling doesn't matter. I'd just turn them off on a nice day so you can work up there w/o dying from sweating!
The key is preparation. AT least dust off the ceiling, walls, and corners. If you have any stains, get a Stain Kilz paint that's latex-based. If the color you're painting over is darker than what you want to paint it now, talk to the paint retailer to see if you should prime first. If you don't, dark paint will 'bleed through' a light top-coat. Buy your paint from a retailer; NOT Walmart or Home Depot or Lowes. (I own stock in HD and don't buy my paint there!) Look in the Yellow Pages under PAINT - RETAIL, and go to one like Finneran & Haley, or Sherwin-Williams, or the like. Get good supplies too. If you skimp on the primer, paint, or tools, your finished job will reflect it! It's not worth the few extra $$$ to skimp.
My best to ya and hope this helps.
PS: Use a latex top-coat. Don't spread it too thin. Plan on 2 coats (tell the retailer this.) The reason I say this is because if you have to ask how to do this job, 1 coat will not look very good. The 2nd coat will cover up any mistakes. You only have to 'cut' once. Just don't skimp. REMOVE everything from the walls that can be removed, and spackle the 'holes'. You can always put them back, unless they're screw holes. In that case, just paint around them very carefully. If you spackle, you will have to sand AND prime for sure! That means dust. Cover everything or try and run a vacume as you sand to collect the powder. Good luck!!!