sanbiz,
Walking is an excellent exercise for low back pain patients. It is great for cardiovascular fitness. Walking will not hurt the discs in the spine.
As to lifting, it is more a matter of how the weight is lifted, than the amount. A small amount of weight lifted incorrectly can cause more problems than a heavy one lifted properly.
If you are going for toning and overall fitness, then lifting light weights many times is the best technique. If one is trying to bulk up, then that is when the max lifts a few reps are done. But, this is usually not recommended for back pain patients. There is no specific weight amount that can be given, as every person is built differently and in different amounts of muscle build. But, in general, using light weights, and doing many reps, is the best way to go.
As to any exercise that would cure a disc bulge, there aren't any. A bulging disc is just the result of the degeneration of the disc. As we age and the discs under go wear and tear, they degenerate. There is no knows way to reverse this process once it has occurred.
The best thing for spine health is to maintain proper cardiovascular and overall general fitness, and to maintain a proper weight. Do not smoke, as nicotine causes the tiny blood vessels around the discs to contract, decreasing the amount of blood and oxygen that get to the discs. This has shown to speed up degeneration.
Good luck.