I also worry about the glass jars breaking. I fill the jars with boiling hot sauce and I hate hearing the ping as the glass breaks from hot in cold. The answer to that is to line the jars up around the pot of boiling water, the edges touching the pot so the glass heats up as well.
Canning is a little scary for me. The whole idea of botulism rather freaks me out, but I try to have faith in the canning process that my sauce will be safe. The biggest keys in canning is to make sure you boil (process) the filled jars long and you don't keep any jars that don't seal. The acidity of the food being canned is key, so follow the recipe you use carefully. Changing a recipe significantly could change the acidity of the food and increase chances of botulism.Have jars touch the pot to prevent them from breaking
Helpful, but not necessary equipment--a rack for the bottom of the pot, a plastic funnel, and a gripper for the hot jarsBefore putting the metal lids on the jars, place them in very hot water for few minutes. This softens the rubber compound on the lids and helps them to seal tightly.
When you process the jars (full of whatever goodie you want to preserve), boil the water uncovered. Because some water will be lost to evaporation, keep a teapot of boiling water handy so you can add boiling water as the water level gets lower. Use boiling water so it doesn't reduce the temperature of the water you are processing cans in significantly.
Processing tomato juice--I need to add more boiling water because of losing some water to evaporation.Using a pressure cooker speeds up the process considerably. I however don't have a pressure cooker so I can't really attest to how that process works or is different.
If you want to can your own foods, I would recommend to talking to someone else who has canned (in addition to me). There is also a good website on preserving food. Check out the National Center for Home Food Preservation. Canning is also becoming a little more popular again. There is a new book out on preserving food and in the Austin area, a class is being taught on canning by the Sustainable Food Center this Sunday.
Watch for my pasta sauce recipe and tomato juice recipe (it's great for Gazpacho!) here in the next few days.