If i take a quick look under my car (fiat punto street, similar to yours) i can see the pipe from the back box running to the front where it attaches to the exaust headers, it are two bolts. so i think if you replace the exaust pipe and back box it should be easy if you can get under your car.
My car has also a very rusty exaust system after only 1.5 years :s i think i will replace it soon ... but i have no experience with exausts so dont take my word 100% for it ^^ hope it helped a little