Do you need a pressure cooker to can home-made salsa?
You cannot preserve just any salsa recipe (unless you're just freezing it).

Tomatoes are on the border between acidic and non-acidic foods. What this means is that they can be water-bath canned if they are sufficiently high in acid; but, if they are low in acid, they need to be pressure canned. 

If you want to be sure to avoid trouble, follow a tested recipe. Salsa recipes will have a careful balance of low and high acid ingredients. Do not alter the proportion of acids (tomatoes and vinegar or lime/lemon juice) and low-acids (other vegetables, peppers, etc). 

The recipe you choose should specify if it requires pressure canning or water-bath canning. One of those two methods must be used, though... you can't just put it in jars and save it. 

For tested recipes, see the Ball Blue Book, the Ball website, or the National Center for Home Food Preservation.