for all your needs on repairing your seicento goto http://www.fiatforum.com and browse the forum its saved me a few quid
You have probs got this sorted out now? But the fuel filter is recessed under the car. It looks like a silver canister or possibly clear under the sill/skirt on the drivers side near the fuel tank.This is all the same from 99-04 but im sure it will be the same for the 06 plate as well... but i cant be sure? Hope this helps??