He's right, there is a big difference between a Pentium 4 and a Pentium dual core that your computer supports. You can buy a pretty nice used CPU on ebay for a good price, much better than your Celeron or a Pentium 4. Just because the clock speed on the Pentium 4 is high, doesn't mean that it's fast. Check out cpubenchmark.net for more information on CPU performance.