OK if you want a stupidly fast Win 98 rig that will max out any games of that era.... And also play early XP games as they were meant to be played..
This based on one of my retro gaming rigs that I built this year
For 98SE/XP games I would recommend a LGA 775 motherboard that has AGP slot. Find one that supports Core 2 Duo or Core 2 Quad. My rig has ECS P4M800Pro Motherboard
Asus P5PE-VM is another good example. There are more. Get the fastest LGA 775 CPU you can find that your motherboard supports.
GPU - Get a Geforce 4ti 4200/4400/4600 This has native DirectX 9.0 support and some games will only work properly on this card or earlier
Only fit 1Gb RAM or Windows 98SE won't work
Fit two hard drives, put Win98SE on one and Win XP on the other. Use the Boot sequence settings in the BIOS to select your OS
Windows 98SE doesn't like HDD bigger that 120Gb. Two 120Gb SSDs is a good choice (that is what I have in my rig)
Get a 4:3 Monitor (I use 19" LCD) or games won't display correct, they will stretch horizontally and look wierd
Get a soundcard that supports EAX for XP games
Get a Voodoo 2 PCI if you want to play early Glide games such as Tombraider 1 or Duke Nukem 3D
If you are more interested in a Win95/Win98 and DOS retro rig, this is my other retro gaming rig
Get a Super Socket 7 Motherboard, I have this one - Gigabyte GA5-AX
Get a fast K6 CPU, Ideally a K6-II+ 450 or a K6-III+ 450 or K6-III+ 550. These run cooler than the non + versions and are easily overclocked.
Fit 128Mb PC133 RAM. More will likely cause problems.
20Gb or 40Gb IDE is plenty big enough.
Get an IDE CD-ROM otherwise you will have problems installing Windows games, or running DOS games
Get a Voodoo 3 3500 AGP, or a Geforce 2 AGP + Voodoo 2 PCI. More recent AGP cards won't work well, if at all, on SS7 motherboards. If you want to look really cool get 2x Voodoo 2 12Mb and run them in SLI mode! remember the Voodoo 2 is an add on GPU, not a standalone Graphics card. This video and the five that follow will help a lot regards GPU choices -
https://www.youtube.com/watch?v=0gipW4lcUHg
Get an ISA Creative Soundblaster (I have AWE 32 ISA)
Get a 4:3 monitor
This won't be cheap to build, but these machines are going up in price year on year, the opposite to a new build!! It's a good investment.
This is authentic period hardware, will play Windows 95/98SE and DOS games perfectly. As it is Super Socket 7 you can disable cache and slow it down to low clock speeds to run DOS games that were meant for 486DX PCs and run too fast to be playable on modern machines
https://www.philscomputerlab.com/gigabyte-ga-5ax-rev-52.html This should help
Also he has extensive GPU test videos on the same platform.
Best online resource for Retro Gaming Hardware advice is Vogons forum.
I hope that helps
Rich