I agree with swaaye. S3 is very comfortable with Dos games and vice-versa. If you wanna use dos games, use s3.
If you wanna use W98 games, use ATI RADEON 9800 XT or PRO.
Games of W98SE era have almost been saturated with 3D technology, unlike nowadays where the fastest card is STILL not enough. So, either GeForce 6800 or Radeon 9800 will do for your W98 Gaming needs. Anything faster or resource hungry games, will rather be run on your WinXP or Vista based newer system.
Just to give you of my current latest configuration : 3 PCs : 1) Classic PC - Pentium 133 with 40MB of EDO RAM, SB AWE64 Gold, LAPC-I, S3 Trio 64V+ graphics card, Pentium MOBO - Baby AT form factor, with a turbo switch to run it slower for more older games. Running Dos 6.22, has Windows 3.1.
2) Windows 98 SE based mid PC : P4 2.8GHz with DDR1 400MHz 512MB RAM, MSI 848P Neo-V MOBO, ATI 9800 XT (AGP8x), Voodoo3 2000 PCI (for those 3Dfx only games), SB Audigy1.
3) Main PC - Q9300, 4GB PC28500, Geforce 9800GTX SLI, ASUS Striker II Formula, X-Fi Platinum, with XP Pro 32-bit in one hard disk, Vista Ultimate 64-bit in another, with 2TB+ HDD space.
Nothing beats a dedicated DOS machine.