
Some poeple have had luck running AGP2.0 gfx cards on AGP1.0/S.Skt7 mobos, but it is risky and full of potential probs and headaches. A 266mhz is VERY under-powered, a K6-III is what you ideally want in there, a K6-III 450mhz would be preferable to a K6-2 550mhz. I take it you are sure that your mobo can accomodate both the K6-2/III and 100FSB. You may very well find a S.Skt7 CPU comes at quite a price and a Duron 1.2ghz would be more than twice as fast as the best S/Skt7 CPU and prob cheaper too, all you would need to go with it would be a SktA mobo using SDR so you can utilise your current PC100 SDRam. This doesn't need much cooling or voltage so you are pretty much guaranteed success providing your PSU is ATX of course. Anyway a 450-500mhz S.Skt7 CPU would enhance your perf greatly but there would be little point going for much more than the entry level gfx cards. I'd suggest Radeon over GF2MX, Rad7500 are very fast and very good all-round cards and they are among the best in terms of compatability and voltage reqs etc.

If you go PCI you are fine to have up to 64MB RAM, RAM size is very important for a PCI card as AGP handles RAM breaches FAR better than PCI possibly can. Expect to be hit a good 20% by using a PCI version of a card, do explore Voodoo cards as these keep more perf going to PCI although you are right about the obvious poor support/drivers PLUS even a Voodoo5 is behind GF2GTS or Rad7500 perf to begin with anyway.

See what price you could get a new S.Skt7 CPU for, then check how much a Duron and cheap SktA mobo would cost you, so long as you have an ATX PSU you are very likely to get plain sailing. If you stick with S.Skt7 then you should find a Rad7500 AGP gfx card will do the trick otherwise a GF2 or Radeon in PCI form will do you no harm and will me a whole world better than a TNT2 M64 or Rage Pro even if you are severely limited by your CPU power.