I don't think you're going to get anywhere near there on that budget. Spending any of it on upgrades will mostly be wasted. Assuming you have at least 2GB of RAM in your system, about the best you'll do is replace the HD5450 with a HD7750 for about $110. I think you'd be a lot better served by accumulating a total closer to $600 and then building an entirely new system.
There are just too many things in your current PC that needs to be upgraded. PSU seems to be a generic brand one which is not something you should trust your components with. CPU is quite weak for gaming. $200 won't get you much at all.