Hi and welcome!
You can find a lot of inspiration from the system specs part of the forums: System Specs
Phil also has done a few videos about Windows 98 rigs, such as this one: Building a cheap Windows 98 Gaming PC https://www.youtube.com/watch?v=5OFaWs136eY
If you don't need DOS compatibility, then you shouldn't have too much issues with sound cards, making a PC compatible with DOS/Win9x/XP is a bit harder although doable, see for example Abit KT7A (KT133A/VIA686B), Athlon XP Mobile 2500+

A good place to start is an Intel 440BX based motherboard. This means a Slot 1 CPU; Pentium III from 500 to 1133 MHz. Use 512 MB of PC-133 RAM, and get yourself a later nVidia Geforce video card that is still compatible with Windows 98, like a Geforce 2 or 3.

Agree with keenmaster486. Slot 1 or socket 370 be your best target boards. A board newer than a socket 478 will be trouble trying to properly run Win98 unless you seek out specifics that still had Win9x drivers. I doubt you will have much luck with a socket 775 though some have had OK success.

The sound card issue is only if you want to run DOS games.
You could even go up to an early Pentium 4 or Athlon XP, so long as there are Windows 98SE drivers for everything. Like 7 vs. 10, when XP first came out there were a few more years where boards were 98SE compatible and many swore they would never upgrade.
Anything with PCIe or > 512MB of RAM is where things get tricky.
Looks like LGA775 would only work if it's very early and has an i865 or earlier chipset. I'd stick with 478 or earlier, or instead an Athlon XP myself. When you get into the waning days of Win98SE you get into another time period, like today, where AMD was compelling.

keenmaster486 wrote on 2020-07-30, 21:50:

A good place to start is an Intel 440BX based motherboard. This means a Slot 1 CPU; Pentium III from 500 to 1133 MHz. Use 512 MB of PC-133 RAM, and get yourself a later nVidia Geforce video card that is still compatible with Windows 98, like a Geforce 2 or 3.

Also a good idea, I have one of these myself. These are also very Windows 95 and DOS compatible, though the OP seems more interested in the later days of 98SE.

MintyFresh wrote on 2020-07-30, 21:09:

I want a system that can run games from Theme Hospital to Morrowind.

Those should run perfectly fine on an current PC, shouldn't they? It may help your focus and motivation if you have something in mind that your current system can't do.

Im not interested in making the pc with parts from the time necessarily, as long as the system runs well and is dirt cheap, Im happy.

Very sensible! But what's dirt cheap in one part of the world might be hard to come across in another, so you'll have to see what you can get. If there's any one thing to watch out for, I might suggest getting something with an AGP slot.

Thank you for all the info guys, very helpful! Theme hospital and morrowind were just examples of the range of years I want to be able to play.
It looks like my best best is the following:
Dell 2Y832 Dimension 4600 Motherboard (socket 478)
Pentium 4 2.6Ghz Northwood cpu
Geforce 6200 AGP gpu
512mb ddr ram
80gb hdd (IDE)
Also, am I correct in thinking that a modern case, fans and power supply will work with all this?

MintyFresh wrote on 2020-07-31, 11:17:

Also, am I correct in thinking that a modern case, fans and power supply will work with all this?

Yep. OS independent.

Worst trouble you might have is if that AGP card needs an external connector (like floppy) that your power supply doesn't provide. But you can grab an adapter if so.

Also I've noticed Molex is um, not a thing anymore so your modern power supply might need SATA to Molex adapters for things like this hard drive.

The dell motherboard doesn't look to have standard front panel connectors but workarounds exist.

This page is going the other way (generic M/B in dell case) but I'm sure you can apply the logic in reverse 😉
https://www.dell.com/community/Desktops-Gener … 00/td-p/4173666

Other then that it's a standard 865 chipset based board. Good Win98 compatibility.
GF6200 is damn fast card for Win98 so will allow you to enable AA, AF, etc and have good frame rates on games that don't run in XP

For sound I'd prefer something with either EAX or A3D support depending on your games list
http://members.optusnet.com.au/kirben/3dsoftware.html

EAX means you want a SBLive! though to a Audigy 2 ZS , As far as Win98 is concerned newer cards offer cleaner sound

A3D 2.0 Your limited to cards with the AU8830 chip most commonly the Vortex 2 cards, these aint cheap!

If it is not about period correctness I can also recommend an Asus A8V Deluxe (The K8V Deluxe works, too). There are drivers for Windows 98SE and I have in fact made such a build for fun.
The build I have had (I only have so much space so my current builds are a socket 1 and 7 system) is an Athlon 64 3200+ with 512 MB RAM and a Geforce 4 TI 4200 on an A8V Deluxe.
It ran everything I threw at it when it came to Windows 98. I got each board and CPU for roughly € 10,00 + shipping so that was very cheap.

Alternatively a Pentium 4 system can be had for very little money, too. Here you can often get boards + RAM + CPU for roughly € 10.00 + shipping, too.
If we're talking about a certain auction site it is often a good idea to not look for instant buy items but for auctions as those are way more realistically priced.

Phil has also uploaded some videos about Pentium 4 and Athlon 64 systems for Windows 98.