The rack is only needed to keep the glass jars off the hot bottom of the pot. You can wire some extra jar rings together to form a rack or use a round cake cooling rack from the dollar store. Some folks use a clean folded kitchen towel instead.
You can use your large pot if it's deep enough to accomodate the rack or towel on the bottom, the jars with the lids and rings that you plan to use, and still have enough room to cover the top of the lids with an inch or two of boiling water. If the lids won't be completely submerged by at least an inch of water, with another inch or so allowance to keep the water from bubbling out of the pot, the pot isn't deep enough.
Do get a jar lifter. After the processing time is up, it is very difficult to get the hot jars out of the hot water without one.
If you don't have the most recent edition of the Ball Blue Book, you won't regret spending the $8 or so on it, it's worth every penny.
