Question 2000'S PC gaming build

Apr 2, 2019
Hi everyone, I'm new to the forums so nice to be here. :)

I've been wanting a retro build for the longest time, so I can re-play some games that I grew up on in the late 90's/early 2000's such as theme hospital and theme park world etc.
I have just bought a pre-built system online, a Compaq Deskpro EN with the following specs as stated on the ebay listing.

866 MHz Pentium III
256 MB RAM
10gb HDD
Windows XP

I will be of course upgrading the ram over time and perhaps swapping the disk drive to either a compact flash or a larger hdd, but one thing I'm a bit confused about is the video card.
I know it is an integrated chip, but couldn't tell you the specs of it.
I know there is an expansion PCI/E slot, but what would be the best video card to put in there? I don't need anything too amazing, after all its just a retro build, but I want a card that will let me pretty much play any game I want from that era.
I don't want to pay too much for it, as I've noticed some Voodoo cards go for ridiculous prices. £200+ on eBay uk.

Anyone have experience with this system? what would you guys recommend adding to it as I'm not new to building PC's, but I am to this specific era of computing.

Cheers, Thomas.