Ok, difference between Intel and AMD;
Basically, AMD Athlon 64s are for gaming, AMD Athlon 64 X2s are for everything else, and Intel Pentium 4s are for video/audio encoding.
Intel has the Pentium 4s which have really high clockspeeds. Compared to Intel, AMD has really low clockspeeds. But AMD does more with what speed they have than Intel. A 1.0GHz Pentium 4 is like a .63GHz Athlon 64. That means that a 2.0GHz AMD Athlon 64 will perform the same as a 3.2GHz Intel Pentium 4. Thats basically what most people don't know about AMD.
Processors have pipelines. Those pipelines have stages. An instruction, sent through that pipeline, has to go through each stage before it's complete. The more the stages, the worse. But you can't have too few stages either. Now, an Intel Pentium 4 (based on the Netburst architecture) has 34 stages in it's pipeline. Thats horrible. Comparitively, a Athlon 64 has 12 stages in it's pipeline. That doesn't mean that the Athlon 64 is 3x faster than the Pentium 4, but it IS faster. Because the pipeline is so long in a Pentium 4, they need to make their processors really fast to get anything done. Thats where the 3.8GHz clockspeeds come in.
AMD isn't some third-party, underground kind of company. Its a perfectly legitimate company. Think Ferrari and Porsche, ATi and Nvidia, Michael Jackson and Unknown Envy. Same basic principle. Except, Intel is a lot bigger than AMD. AMD only has like 17% of the market. But you know what the funny thing is? AMD has stronger, and better, processors than Intel.
But that was all the boring stuff. AMD is definately better at gaming. A Athlon 64 3200+ (2.0GHz) may be the same as a Pentium 4 3.2GHz, but thats only in normal tasks. In games, AMD is far and away, the best. An Athlon 64 3200+ (2.0GHz) will probably beat a 3.6GHz Pentium 4 in most games. In Battlefield 2, a Athlon 64 3200+ beats a 3.8GHz Pentium 4.
Intel is often more expensive than AMD. Pentium 4s also run REALLY hot compared to Athlon 64s. And Athlon 64s overclock farther, generally, as far as home overclocking goes.
Intel is putting out the Conroe, and Conroe has a 14-stage pipeline so if you learned anything from this post, you'll know that it'll be good. Thing is that Conroe's 4-issue Core makes it perform much better than the Athlon 64. So a 2.0GHz Conroe = 2.4Ghz Athlon 64 (atleast thats what Intel claims, and a recent benchmark at IDF more than proved that).
If building a PC anytime before Q4 of this year, go with AMD.