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Well, try to teach him, maybe even show him some benchmarks + pricewatch prices. If that doesn't convince him, let the pricetag and performance of your Athlon XP smoke his equally clocked (yet more expensive) P4 
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Here's a nice way to teach the n00bs about the AthlonXP

It's taken from AMD's quantispeed tech-doc:
AMD Athlon? XP processor with QuantiSpeed? Architecture Analogies:
1. Adult and Child Walking
If a child and an adult are walking together, the child needs to take more steps to keep up with the adult. Since the adult has a longer stride than the child and travels further with each step. The child has to work harder?by moving faster?to try and keep up.
2. Automobile Engines
Two cars are in a race. The Blue Car has a 6-cylinder engine while the Green Car has a 9-cylinder engine. While the Blue Car?s engine works hard in terms of high RPMs, it doesn?t actually go all that fast down the road. In contrast, the Green Car?s more powerful engine doesn?t have to run at high RPMs. Yet on the road, the Green Car blows the doors off the Blue Car. The more powerful Green Car engine is designed to run efficiently and to deliver a faster, more powerful driving experience.
3. Bucket and Cup
You and a friend are out on the lake in a rowboat. At some point, you both notice that the boat is taking on water. Your friend starts bailing water with a cup while you start bailing water with a bucket. In a panic, your friend bails faster than you, but since your container is larger, you end up bailing more water in the same amount of time.
4. Cycling
Two cyclists ride together on 10-speed bikes. One cyclist uses the 10th gear, pedaling slower but moving faster down the road and covering more distance with each stroke. The other cyclist uses 1st gear and has to pedal like a lunatic to achieve even close to the same speed on the road and cover the same ground.
AGodspeed, I thought I was the biggest AMD zealot till I met you

(I trust you understand that's a compliment)