The stock cat-back can be removed without cutting the tailpipes (just at the exit of the mufflers) but it requires taking the lower control arm off and dropping the axle enough so the muffler/tailpipe assembly can be manouvered out. Most people just cut the tailpipe (hacksaw or sawzall or grinder w/ cut-off wheel).
It can be tricky just getting the right position of the mufflers and tailpipes so don't tighten everything up immediately. Put it together loosely and check for clearance near the driveshaft, gas tank, and axle/shock areas. Remember that you can rotate the whole assembly clockwise/counter-clockwise (as seen from the exhaust outlet) to maximize clearances. Take your time and be prepared to jack the car up again if you hear some rattling or clunking during the test drive.
The kit comes with u-clamps. You can buy band clamps (about $8 each!) and they will not crimp any of the joints. You can have the whole thing welded up, too, if you want. After a week or two of driving (a bunch of heat-ups and cool-downs), recheck the clamps because they will loosen after a few cycles.