1GB will work for sure. Then again it's your choice. If you asked me about the risk, I'd say it would impair your CPU (slightly though), if not causing Overheating. Also multi-tasking would be stagnated greatly, especially when using hacking program.
On your graphic matter in Grand Chase, there are 2 things that I'm certain
1. Your graphic card can't handle graphics that many layers of "Monster Freeze" use. No matter how you look at it, 512MB won't do
2. You ticked "Auto Adjust" in the Graphic Configuration in Grand Chase. You can turn it off to solve this problem.
