Honestly I wouldnt recommend spending R2000 (if you can find one that cheap!) on a graphics card for StarCraft II - it just isnt that graphically intensive. What resolution do you play at? Even a 5670 would be fine for it!
The problem is that you might struggle to update your PC because so much of it needs updating. Your CPU does need updating, because unfortunately it is a Dual Core and not a Core 2 Duo, thus it is akin to a Celeron (it has less L2 cache) and thus likely somewhat under the official recommended spec of a 2.4 Ghz dual core. See the official recommended specs here.
As you will read on that page, a 1.8Ghz Core 2 Duo just barely manages it while a 2.4 Ghz Core 2 Duo is recommended. Thus, your CPU needs an upgrade.
If I were you, I'd upgrade PSU, CPU, Graphics card, RAM, and Windows, in that order. You'll struggle to keep it under R3k admittedly. A new case and mobo would be nice, but are outside of your budget. If you can get a 4850 for cheap, get one rather than a 5670.
The problem is that you might struggle to update your PC because so much of it needs updating. Your CPU does need updating, because unfortunately it is a Dual Core and not a Core 2 Duo, thus it is akin to a Celeron (it has less L2 cache) and thus likely somewhat under the official recommended spec of a 2.4 Ghz dual core. See the official recommended specs here.
As you will read on that page, a 1.8Ghz Core 2 Duo just barely manages it while a 2.4 Ghz Core 2 Duo is recommended. Thus, your CPU needs an upgrade.
If I were you, I'd upgrade PSU, CPU, Graphics card, RAM, and Windows, in that order. You'll struggle to keep it under R3k admittedly. A new case and mobo would be nice, but are outside of your budget. If you can get a 4850 for cheap, get one rather than a 5670.