I won't question your desire to use 64-bit PCI as we have been building an ever larger number of 66MHz PCI bus systems in the past 6 to 8 months. Most requests come from people that want to exploit the dramatic performance issues relative to both multimedia workstation and high performance server configurations.
There are actually quite a few choices now, here a few:
Asus CUR-DLS, Dual P3 - FCPGA, with ServerWorks ServerSet III LE 3.0 chipset, up to 4GB PC133 HSDRAM and LSI 64/32-bit Ultra2 SCSI.
Tyan Thunder 2500 motherboard (S1867DLUAN) using the Server Works (RCC) Server Set III HE chipset. Dual Slot 1, 100/133 MHz FSB, supports up to 8GB Memory in matched pairs (ONLY), 1 AGP 2x , 6 64bit PCI, 1 shared PCI/ISA slot(s). On-Board U2 SCSI, Sound, LAN. It's a monster using the Extended ATX Form Factor.
Tyan Thunder K7 (S2462) having dual-processor platform support for the AMD Athlon MP processor. Too many features to list here, this is now my favorite.
Gigabyte GA-6EXDR using the ServerWorks ServerSet™ III LE Chipset. This is a rack-mountable motherboard.
Gigabyte GA-6ETXDR Supports Dual Intel Pentium III Coppermine and Tualatin socket 370 CPUs using the ServerWorks ServerSet III LE Chipset and the LSI Symbios 53C1010-66 Chipset.
Intel Server Board STL2 for Intel Pentium III Processors uses ServerWorks ServerSet III LE Chipset, or the even better Intel Server Board SBT2 for the Intel Pentium III Xeon Processor.
On the Alpha front, you can also checkout, http://www.alpha-processor.com/. They have a few motherboards using 64-bit PCI.
We've built systems using all of these boards. I have to say that at this time, I really like both the Alpha based products as well as the AMD 761 based Tyan board. I personally think the ServerWorks chipsets are pretty sluggish. While they give you the features, the performance is not what we expected to see, but again, that's just my opinion.
There are other boards out there as well, but I've only listed the boards that we have tested and used.
Good Luck
Steve Benoit
Stable Technologies
'The way IT should be!'