If you want to use PCI card look for `Fujitsu Siemens Futro S400`: https://www.parkytowers.me.uk/thin/Futro/s400/
It has the same CPU and chipset as HP T5720 (tested by Phil) but it is IMO a better choice because:
* Case is big enough to install one of these chinese GeForce FX5500 PCI
* You can install CF card inside, additional adapters are not needed (16 GB Sandisk card didn't work for me, but 4 GB Transcend was fine)
CPU performance is on level with P3 or Athlon 1100, so it should be more than enough for games released till 2002/3.
P4 3.4E, ASUS P4C800-E Dlx, 1 GB, X800 PRO 256 MB AGP, SB Audigy, XP SP2
P3 800, AOpen AX6BC, 128 MB, GF2 PRO 64 MB, ALS100+, 98SE
P233MMX, MS5149, 64 MB, Virge 4 MB, V1 4MB, ESS1868, 95 OSR2