I was checking online for something to make my Honda 2001 faster and I ended up with a new exhaust system. The best one I found was a catback exhaust built for a 2000 Honda Civic DX/LX and I have a 2001 EX. Does anyone know if that will fit or should it be left to its owner?

no, it will not fit, they are completely different cars, there are many cat-backs made for the '01, here is a rather extensive list of the ones available http://www.nopionline.com/nopistore/dsp_part_detail.cfm?vmakeid=140&vmodelid=020&vcatyear=2001&vnopinum=001%2B3357&vTitle=HONDA%20Civic%202001