Yeah, 512MB is the way to go, two sticks of 256 in that mobo lets you go dual channel.
I don't remember what OS you're running, but I wouldn't bother with 512 if you've still got 9x anything. BTW, Durons overclock really well if you get one that isn't locked... Oh course I'm being overzealous since you haven't even mentioned upgrading...
BTW, the 128MB on your video card is like strapping a 3 foot spoiler on a Ford Tempo... There should be 64MB on that card tops...
<font size="1">*grumble*
...stupid greedy marketing bafoons... *grumble*</font>