From my quick web searching, I’ve determined you have either 256 mb or 512 mb or DDR2 RAM. In my opinion, this should be upgraded to at least 1 Gb (make sure what you buy is DDR2 RAM because there are other kinds like DDR and DDR3). This is definitely slowing down your computer if you are gaming. Personally I have 2 Gb, and therefore I am confident my RAM is never my bottleneck that slows my computer down. Most high end systems that I know have 2 GB to be sure… more is getting a little ridiculous I think.
Your processor isn’t great, but since you probably will have a hard time upgrading it (money, and its probably not worth it without a new motherboard) I suggest checking the processes tab in the task manager and stopping programs that 1. you recognize, 2. you are sure don’t need to be on. You don’t want to stop processes you don’t know, that could be bad. For example, ituneshelper is usually constantly running in the background of my computer even when itunes isn’t running. So I shut it down. Shutting down processes like this will lessen the strain on your cpu and open it up to gaming.
theres other things you can do, but you’re probably bored by now so I’ll stop. If you want me to continue or clarify, please ask!