Untrue, if you're comparing a Celeron (D) to a Pentium (4), then the only differences that make it a worse performer is it's very low amount of cache, and slow FSB, it also didnt have HT.They dont have a maths processing chip or something like that so the performance is fairly bad for anything other than word processing, surfing the web and other low power tasks.
I would advise getting a core 2 duo or atleast a P4. What celeron is it? You should be able to get a processor that fits in your board. Though you might not want to of course.