Hmmm...for the sake of narrowing things down, I'll assume you don't need/want a dual-CPU system. Here are your choices:
1) The Pentium IV
First of all, the reason sales guys are telling you all these different things about the Pentium IV:
There are currently two "socket formats" for the Pentium IV, a 423-pin socket ("Socket423") and a 478-pin socket ("Socket478"). Socket478 is the newest socket format, and you should generally expect that future speed grades of the Pentium IV are going to be Socket478.
There are currently two basic motherboard options available for the Pentium IV. One is the i850, which uses high-performance (and expensive) PC800 RDRAM memory, and typically only works with Socket423 CPUs. The other is the i845, which uses older, slower PC133 SDRAM memory, and typically only works with newer Socket478 CPUs.
Just about anyone here will tell you: the i845 solution is not worth buying, simply because the PC133 memory kills its performance. The i850 is the motherboard of choice for the Pentium IV, except that I have yet to see one that supports Socket478.
So your options for Pentium IV are:
i850+Socket423
decent performance, but no definite upgrade path.
i845+Socket478
you have an upgrade path, but you get crummy performance.
I know that sounds like a sorry state of affairs--let me be the first to say that it shouldn't be like that. It's just the mess Intel has gotten themselves in lately. AFAIK you currently can't have the best of both worlds with the Pentium IV.
I've heard rumors that there will be a "socket converter" to allow Socket478 CPUs to work on Socket423 motherboards, but nothing definite.
Also, if you get a Pentium IV+i850, don't let a sales monkey fob PC600 RDRAM off on you. PC600 performs badly; demand PC800 RDRAM.
2) The Pentium III
This is a rather old CPU, but it's good for quite a lot. It has the advantage that it doesn't need PC800 RDRAM to perform well. It uses a socket format called Socket370. It generally doesn't perform quite as well as the Pentium IV though.
Older speed grades of this CPU (1GHz and slower) will work on just about any Socket370 motherboard currently manufactured. Newer speed grades (above 1GHz, known as Tualatins) require a Socket370 motherboard designed for Tualatins.
Has a stripped-down, "economy priced" little brother called the Celeron. Celeron will generally work in the same motherboards as a Pentium III.
3) The AMD Athlon "C"
The latest CPU from AMD. Outperforms the Pentium III and performs roughly on par with the Pentium IV. Costs less than either one. Current best motherboards for the Athlon "C" are based on either the AMD761, ALi MAGiK 1, or SiS 735 chipset. Athlon "C" can generally perform well with PC133 SDRAM, but performs best with PC2100 DDR SDRAM. Generates twice as much heat as a Pentium III, and (AFAIK) about the same amount of heat as an equivalent Pentium IV. Can be a hassle to upgrade or build yourself, but generally no problem if you buy a pre-built system from a good retailer.
Has a stripped-down, "economy-priced" little brother called the Duron. The Duron will work on pretty much any motherboard where an Athlon "C" will work.
4. Cyrix/VIA CPUs.
Forget it. They're really not worth it unless you get one for free. You're better off committing ritual suicide with a cell phone and a liquid lunch. :tongue:
That's about it for what you can get--next thing to ask is, what do you need?
Games and basic office apps do just fine on a 1GHz Athlon "C" or a 1GHz Pentium III. Pentium IV is not necessary, and really, you can do well with a CPU that's slower that 1GHz, either Athlon "C" or Pentium III (or even their little brothers, Duron or Celeron).
For compile jobs and 3D render jobs (which can take hours), an Athlon tends to beat everything else. For MPEG 4 (DivX) encoding (which can also take hours), the Pentium IV excels over everything. If you're into any of those sort of activities, you should base your purchase on that.
Kelledin
"/join #hackerz. See the Web. DoS interesting people."