The Sempron 3400 won't be a problem: I'm working on a Sempron 2600. The two things to watch are your small memory and the NVIDIA video chip.
With 512MB, you can use (with a reasonable margin of safety, for distros tend to grow)
Xfce desktop: Mint, SalineOS, Salix
Mate desktop: Salix
LXDE desktop: Mint, Salix, WattOS, ZorinOS Light
Enlightenment window manager: AtlasX, Bodhi
ICE window manager: Swift
Search at their forums or here for any advice they may have on setting up with your NVIDIA card.
You may find that your browser's Flash plug-in doesn't work. If that's the case, the answer is here: