I am in the process of killing the grass in my small front lawn by putting down newspaper and covering it with bark mulch. I had understood that when the grass was dead, I could then punch holes in the newspaper and plant wildflowers or ground-cover plants. Someone else has said that the bark mulch will kill anything I plant. Any thoughts?

A few years back I received a wildflower mix from a company which specializes in same.Their directions for planting were very detailed and required total removal of existing vegitation,and rototilling the area.
I had no luck! Recently, however, I witnessed someone who just sprinkled seed on the ground and had success.I would remove the mulch in the spring,plant,and see what happens.I do know that leaving the mulch down will tend to make any new plants have shallow and unstable root systems.

I don't know about the bark mulch part, but I can tell you that the newspapers will disintegrate in time with no harm, and you don't have to worry about punching holes in it. Just use a couple of layers of paper, not a ton. My wife has done this in several beds around our house using LEAF mulch and leaf compost. You have to pay attention to what you plant, as it must be something that "likes" that acid from the leaves.
I suspect that bark mulch alone will not support much of anything. You need some soil or compost.

Bark mulch is very acidic. Try a hardwood or cypress mulch.you can simply use a weed and grass killer like "round up", this doesn't harm the soil. then once you see the seeds break use PREEN a weed preventer around them this will keep the flowers but prevent weeds from coming in between them. As for even needing mulch, you don't have to have it, all it does is keep the ground moist, just water the area once a day and they will grow in any decent soil.