Everyone keeps telling you that your mobo/memory performance is unacceptable. But consider this a little closer:
Assume all other things being equal, if you just got faster ram and nforce 2 chipset mobo will that improve your gaming by more than 5%? No. Upgrading from KT266A/333/400/600 to an Nforce 2 mobo will give you a boost of maybe 2-3%. And since buying PC3200 ram will allow you to run your memory at 266 but at lower timings expect another 2-3% maybe. Now what is the cost of a good nforce 2 mobo and ram? AS much as a 9800Pro videocard. What would give you most bang for the buck right now? surely it is the videocard, not cpu, not mobo, and not necessarily faster ram, but more ram to 512.
Of course the recommendation to buy PC3200 is because you will be able to reuse it later for say A64 platform for the next 2 years -- should be still a standard. I think your best option right now would be to get 256mb PC3200. Socket 939 A64 is dual channel so it will probably have at least 3 slots. So you can then take this 256 and either get another 256 + 512 later to run them in dual channel or if it has 4 slots then you are in heaven cuz u'll be able to get a lot of ram. If you have some $$$ i'd definately go for 512 right now because 256 sticks are nto the best option. Then like you are thinking get the 9800Pro when the prices come down and use this rig for the next 4-5 months or how long it lasts. Then you simply do a full switch to A64 platform and forget upgrading to AXP or 478 sockets right now as they are dying. Hopefully they'll have a motherboard that has both AGP and PCI-express on board.
Also ask yourself how terrible is the lag in games? In which particular games is the computer lagging? It could be that if you play a lot of CPU intensive games only, all i've said above is not important. But if you play Halo, Far Cry, and other shader intesnive games, you can forget the cpu upgrade as that will do you no good. But like others have said about upgrading the chipset because your mobo is too old, that is a bad advice as that will not give you any negligble performance upgrade.
So either A) do a complete system overhaul in 6 months (right when hopefully Doom III, STALKER, and Half-Life 2 come out, socker 939 and 775 will be free of bugs and prices will have fallen on the old and even some new cards for sure)
B) get either 256 or 512 ram (at least PC3200) right now, and a 9800Pro. The only problem i have is that I think in 6 months even 6800 $299 will be about $220 so the Radeons will have to drop to about $120 or it will be unreasonable to get old technology. Of course then if you buy it now at $200 you'll lose some money as a result and speed. But I cant tell how slow the games run on your computer and just how badly you need this upgrade now......