Well, I was in the same situation as you a while ago.. moving from AMD to P4 out of a mix between curiosity and the fact that I believe the P4 is gonna be a bit more scalable down the future than the K7 will be.. that, and I wanted to give an Intel chip + Intel mobo a shot. Via's little quirks.. not instabilities.. but quriks in their chipset have been affecting me lately, and it's driving me crazy.
Well, as for mobo, do ya wanna do RDRAM, or DDR? If you're going DDR you have the SiS 645DX, and the i845D, E, G, and GL. I'm omitting Via due to the fact that I didn't really research them much.. Via + Intel makes no sense whatsoever IMO. 😛 The SiS 645DX is supposed to be a fast, solid chipset supporting 533mhz FSB at a good price. Intel's 845D chipset is the original 400mhz DDR solution. E is an unofficial 533mhz DDR solution, but most people op for this one as explained later. G is the E with official PC2700 support and integrated graphics. It seems the graphics limit the overclocking abilities of these boards a bit, so most people op for 845E at the time. Not overclocked, however, I believe G is currently the fastest. GL, I haven't gotten to read much about it, but it seems it's kinda like the mini-ATX version of the G chipset.
If you're going RDRAM, I have no idea.. if you're going DDR, the MSI 845E Max mobos are nice.. and the barebones one is pretty inexpensive too. Asus has some nice boards, but they're pretty pricey. I found my price/features/performance combo in the Abit BD7II. $118 for i845E, Abit quality, and integrated LAN. Not bad. From the looks of what people have been saying, it needs a couple BIOS revisions to be *perfect* though.
Best chip - matters what your budget is. A good mobo and 1.6A can be had for $250-270 at Newegg, and 1.6A's have been known to break 2ghz regularly. With a 533mhz board, you can always ditch the 1.6A when it starts getting a little slow and upgrade to something new as well, so.. 1.6 should be good, IMO. If you want a little more speed, you could dish out the extra few bucks and perhaps go for a 1.8. Again, I don't know the budget.
As for RAM, it matters. It's possible to overclock to 2.0+ with PC2100 RAM, but if you want to use ratios other than 1:1 at 133-140mhz FSB, you're gonna want to pick up some True Samsung PC2700, or if ya really want a sweet overclock, you could go for some pricy, yet nice, Corsair XMS3000. Other nice brands are Crucial, Kingston, Mushkin.. the usuals.
I hope some of this might help. As for ratios on CPU to RAM, you'll need to ask someone else for the details, but it's basically the act of running the CPU and RAM asynchronously, at an FSB to RAM speed ratio, like.. 3:4 or 4:5. To simplify it, think of, say, 3:4 as, when ya bump up your FSB.. you're bumping the CPU up 1mhz, and the RAM up by 1.33. Sorry if what I just said makes no sense. 🙂
This is kinda all my knowledge I've gained in the last couple weeks on my crassh course in P4's.. so.. hope it helps ya. 🙂
