Early to mid 2000s on a P3 with 256MB of RAM, a Rage 128, and Win98 capping you out at 512MB of memory? Not a recipe for success imho.
Should be more like Pentium 4, AthlonXP, or Athlon64 with 1-3GB of RAM, WinXP, and GeForce FX/Radeon 9 just to start. Mid 2000s you're talking games like Oblivion (2006), Doom 3 (2004), Half-Life 2 (2004), Hitman 4 (2006), Age of Empires 3 (2005), etc which will happily take a GeForce 6800 to its knees depending on settings and resolution. Ideally you'd step a year or two beyond and have a Core 2 or Phenom, and GeForce 8 or Radeon 2k series to ensure everything will run swimmingly with high settings. Games from the early 2000s like Halo and Morrowind will happily come along for the ride on such a system, but a few of them (like Morrowind) won't like Windows Vista or higher, which is why I'd stick to XP.
For early 2000s I'd still regard the P3, 256MB, Rage 128, etc to be mostly inadequate - it will struggle with a lot of things, especially titles that want TnL, PS support, etc. The Rage 128 is the biggest problem as it sits (its anachronistic - it's a DX6 card from 1998/9), the 256MB of memory is the next biggest problem, and then the CPU after that. If you have to keep this P3 system for whatever reason, I'd suggest at least upgrading to a GeForce 2 or Radeon (more ideally GeForce 3 or Radeon 8500 to have TnL and PS support), maxing it out at 512MB, and upgrading to whatever the fastest P3 the board can take. Alternately, reduce your upper chronological boundary - 2001-2002 is probably realistically the upper limit for most games on the machine you've outlined (and many of those will run at low settings, low resolution, and may still drag), but it will be MUCH more comfortable in the 1990s.
Another thing to consider - I've yet to have a DX9 title refuse to work in WinVista or higher (although there's currently a discussion on Vogons about FarCry having some graphical oddities under Vista+), so if you have a modern (even semi-modern) gaming system running Vista/7/8/etc it should have no problems with mid-2000s games, and if you're just meaning to support things that are having trouble with the newer OS, this P3 with a better graphics card, more RAM, etc may be just the ticket.