To run everything smoothly you need at least an AMD Athlon or Intel Pentium III, 512MB RAM, a video card like the original NVIDIA GeForce and Windows 98SE. You can get anything more powerful than that, assuming it has Windows 98SE drivers available, since this is a must. My sisters laptop (Pentium-M Dothan 2.1, ATI mobility 9700Pro, 2GB RAM) is one of the last that had Win98 drivers and I have a spear HDD for WIN98 to use with it
At those times I personally had a socket 7 with K6-2 550 and a s3 savage 4. This was lagging big time in 1999 games and was notably slower than my friends (Intel Celeron 433, Riva TNT2 M64)