Built myself around what I had lying about and ended up with a really good gaming Windows 95/DOS system.
MB: Micronics M55hi+
CPU: Intel Pentium P54c 200MHz
RAM: 64MB (16MBx4 72-pin SIMMs) 60ns EDO
MB Sound: Creative Labs Vibra16 (SB16 chip, ISA bus)
PCI1: ATI Rage IIc 2MB
PCI2: Diamond Monster 3D 4MB Voodoo 3D Accelerator
HDD: Maxtor 20.4GB IDE (using drive overlay software)
OS: Windows 95
It works really well with later-era DOS games that aren't speed sensitive and early GLIDE games with the Voodoo1 card. I got a pass-through off of the internet and it works incredibly well as a replacement for the cables nobody ever seems to want to sell with their original Voodoo cards.
Since the system was being built around the MB and CPU limitations, I planned the build around 1996-1997, which actually meant for me downgrading to Windows 95, installing DirectX 5/6/7, the OSR2 pack, etc. The fun part was getting DOS configured correctly to work out of the box with just about any game. With 64MB to work with, I was able to not only load DOS into high memory area, freeing up to 614KB of conventional memory, I also have both 8MB of Expanded Memory and the rest is Extended Memory, so both types of DOS games will work without the need for selection programs like Phil likes to use. I also have working CD-ROM and MOUSE drivers at all times, whether they're needed or not.
Honestly, for early Windows 9x gaming, 64MB of RAM is overkill. Hell, 32MB would have been a cherry sweet-spot for gaming. I used to run Windows 95 on an early Packard Bell with only 16MB of RAM and it worked fine, though not as a gaming machine because of its restrictive 100MHz Pentium and lack of any dedicated 3D graphics hardware.
Now, compare that to my 1999 gaming rig, which is a totally separate system.
MB: ASUS P2B Revision 1.02
CPU: Intel Pentium III 600MHz Katmai Slot-1, 100MHz FSB
RAM: 256MB (128MB x 2 DIMMs) PC-100 SDRAM
AGP: Diamond Viper V770 (NVIDIA Riva TNT2) 32MB
PCI1: STB V2-1000 12MB Voodoo2 3D Accelerator
PCI2: STB V2-1000 12MB Voodoo2 3D Accelerator
PCI3: 10/100 Ethernet
ISA2: Creative Labs AWE64 Standard
HDD: Western Digital 40GB IDE
OS: Windows 958 SE
As you can see, stepping forward a few years into a Pentium 3 chip, I can now push more graphics horsepower properly, so I've front-loaded this system graphically, with a TNT2 card (NOT the M64 version) and dual Voodoo2 cards in SLI. This is a gaming beast by 1998/1999 standards and plays most games of the era flawlessly. Half-Life is buttery smooth, using either the TNT2 or the Voodoo2 cards. Unreal, Quake 1&2...all liquid. And this is without a 1 GHz processor.
The system shows its age with later games like Return to Castle Wolfenstein (FPS drops below 20 sometimes, noticeable stuttering in heavy action scenes), a basic inability to run Morrowind, even though it meets "minimum" system requirements, things like that.
I would agree with the earlier posters. Either center your system around that 166MHz CPU by dropping your expectations of the graphics and sound hardware or step the whole thing up by dumping the CPU and replacing it with a much faster AMD chip at or near 500MHz.