Let me say this and this is my personal experience. I just recently built a P4 1.6Ghz system on an ASUS P4T-E board, that is based on the I850 Chipset, with 512MB of RDRAM and this is BY FAR AND ABOVE the MOST rock SOLID system I have ever seen. I am running Windows XP Pro and it is smooth as glass.
I built a comparable system with an Athlon processor on an ASUS A7V board, which is based on the VIA KT133a chipset, with 1GB of PC 133 SDRAM and 1.2 Ghz Processor. Video Card was the same on both systems, Leadtek GeForce 3 TI, and that system would not run XP very well AT All.
I'm not bashing AMD...I Like AMD and that box smokes with Windows 98 and is pretty stable...Within 98's limits, but after a little while of any amount of multitasking, or running Photoshop, I had to reboot. It was just Windows 98 poor memory management IMHO.
My claim is not the only one...there are literally hundreds of posts in the alt.comp.periphs.mainboard.asus newsgroup that all say the same thing.
I also realize that there are many other fine boards/systems out there. Gigabyte, Abit, Soyo Dragon, there's a bunch. The one thing I would suggest is that you do ALOT of research before deciding which way to go. Read the message boards and newsgroups, see what problems people are having with their systems/mainboards, how easy it was to solve. Check out the manufacturers support site...How thorough is it?
Yes, RAMBUS is expensive and does have to be installed in pairs, but I only spent $180 on my 512MB of Corsair. The other caution about RAMBUS modules is to make sure they are IDENTICAL in every way between that pair (i.e. same number of chips), otherwise the system may not even post. I Saw alot of that in the asus newsgroup too where the manufacturer had shipped them mismatched RAM and when installed the system wouldn't post.
Another thing, if you do go with a P4 system then make sure you go with the socket 478 board so that you are guaranteed upgradeability. Socket 423's are being phased out from what I understand and the Northwood P4's are all socket 478.
I'm sorry to have rambled on so much.