Re: painting ceilings
Lead is not the problem.
If you've got stains, you've got to completely seal them in or they will continue to bleed no matter how many layers of paint you put over them. I would recommend switching to a pigmented shellac, it will seal better than Kilz and IMHO it's easier to work with.
Apply at least two coats, more if the stains are particularly heavy. You may want to spot prime the bad areas several times before coating the entire ceiling twice to blend it all together. Once the primer is on and dry, you can apply your top coat.
Another tip: Once you've primed the spots and entire ceiling to your satisfaction, you may want to leave it for several weeks. If the stains are going to continue to bleed, they'll start reappearing and you can knock them back with the primer again. Repeat until you're satisfied you've stopped the bleeding, then follow up with two coats of your top coat paint.
I suffer from CDO ... Its like OCD, but in alphabetical order, LIKE IT SHOULD BE!!!