yout limited by the Q8200 (if thats what your using), and 7gb DDR2 wtf USE MATCHED PAIRS FOR DUAL CHANNEL, more ram can actually DECREASE PERFORMANCE, also dump xp and do a solid windows 7 64 install comeon seriously, and i hope your "550 watt power supply" is a branded psu.
Some of us still need XP for programs that will not run under Win7. Even in the XP mode of 7 so ditching it is not an option.
Some of my older games I stiip play occasionally will not install or run after installed. AOE will run but has seriously screwed up colors. trees are red etc.
Also my credit card processing software will only run on XP. so ditching XP is NOT an option.