I see a few areas where you could use improvement.
1.) If you're, "into gaming" you're videocard absolutely needs to be upgraded. A 6800GT would give you a good boost in performance without leaving cobb-webs in your pocket.
2.) By todays gaming standards, "512MB" of RAM isn't going to cut the cake. Upgrade to at least a GIG.
3.) If you only have one HDD, consider picking up another and use it as storage. Move all of you critical files over to it. Then give your primary a full format and reinstall your OS and all your drivers and essentical programs. After a fresh install, keep your primary HDD with your OS & DRIVERS & PROGRAMS Defragged and light. Use your secondary (if you have one or purchase one, for all of your media files, backup files, game saves and paging file.)
4.) If you do go into your case and upgrade, take the time to completely clean out all dust and debris with a can of compressed air.
5.) Investigate your system, cpu and vga temps. Download "motherboard monitor 5" or use a similar temp. monitoring program to make sure your system components are operating at a safe temp. Overheating is one of the largest causes of poor system performance. Also the stress that it causes components lessens their lifespan.
6.) Of course after format and reinstall, protect yourself with the proper, "adware, spyware and virus" protection.
There are a few other things, but you should start with these.
You've got a nice CPU and should be fine in that department. IF you do decide to upgrade a few mentioned components, make sure your PSU can handle the upgrade. 400-600w PSU's are becoming more and more the standard for a good gaming PC.