Wow, super cool, Love the older systems, Now the AMD 3000+ is not a bad chip, does overclock as well easily to 2.3ghz even with stock cooler if the Mobo allows it, enough ram as well, I guess the thing is how much longer you will keep the system and how much is it worth spending the extra money on a graphics card for it, Now the 1650 Pro is definately a step up on the 9600 and you will notice a difference, and for the amount spent its a worthwile upgrade,
here is a good example on new-egg
http://www.newegg.com/Product/Product.aspx?Item=N82E16814102073R
I think though the 1950 pro is far far superior than the 1650 but a lot more expensive, now it rocks for DX9 on Windows XP but s not DX10 capable, which is not a problem if you never plan to run Vista on that Box, the downside is that it needs 36 Amps on hte 12 volt rails, (2 molex connectors to power it ) which means you need at least a 550 watt generic powersupply that has dual 12volt rails, i had one of these with my old P4 socket 478 and needed to upgrade the power supply to get it to run,
Here is a good example of one
http://www.newegg.com/Product/Product.aspx?Item=N82E16814129077
But saying that, I think if you are to do the upgrade on your machine then this has to be the card for you, Inbetween the two in price and a good card to boot, the newer 3650, it has definately got more oomph than the 1650 and does not need a small nuclear power station sat along side just to power it, its quiet and DX 10 to boot if ever you do want to play Vista or Windows 7 and its not that expensive if you were looking at $80 for a 1650 It will play all the games you specify at 1280x1024 and maybe a few of them with the eye candy above medium and definately AA on far Cry (Still better than Far Cry 2 in my opinion, game has a point, Far Cry 2 go here kill go other side of map, kill some more, and kill everyone inbetween and do that till 100% game complete lol)
here is a good sample of this card
http://www.newegg.com/Product/Product.aspx?Item=N82E16814102814
Overall, I think the CPU will slightly bottleneck the 1950 and 3650 but not so much that you notice it on 1280x1024, the real slowdown on your pc would be games that cane the AI such as Real-Time Strategy games and even things like Colin Mcrae Dirt or Need for Speed Pro Street where a single core just does not have the speed necessary,
Over-all I would go for the 3650
Please Peeps feel free to put in your input on these choices