kia that pops

i have a 2000 kia and it makes a poping noise kinda like backfiring we think it may be the fuel filter, fuel sinding unit, or the fuel pressure regulater its very urgent i need you help

...How does that translate in the general behaviour or the car? Is it just funny noises like occasional backfiring or are there other symptoms, like loss of power, hard starting, stalling...
These cars are notorious for their oxygen sensors going haywire....check this as a start
http://avigex.ca/kiasport/components.jpg