PCIe was not made until 2004, and widespread use did not come for a few more years. I don't think any Socket 478 motherboards have PCIe slots.
OP, you need an AGP video card. My old Pentium 4 machine has those specs and had an ATI Radeon 5200, which you might be able to find used online. But since that hardware is over 10 years old, you won't find it new anywhere. And $50 even is a steep price, so go out of your way to find good deals. (Like, $20 or less IMO)