You can safely tell them they don't know what they're talking about. ;-)
An unlocked PII 550 @ 3.33GHz would be roughly in the range of an X4 955, which is just about the equal of a Core 2 Quad 9450:
http/anandtech.com/bench/Product/88?vs=51
On the gaming front, your CPU will be able to keep up with much more expensive Intel chips, as many benchmarks will show.
Hopefully you have a solid GPU to back it up. Then all you have to do is crank up the resolution and watch your ignorant friends' jaws drop in disbelief.