Like @gamerk316 said, your PC is far from the front lines of hardware right now. Although it's not super-bad -- still #6 on the hierarchy (http://www.tomshardware.com/reviews/cpu-hierarchy,4312.html), not bad for an 8-year-old CPU -- your system needs some upgrades.
Before some suggestions, though, what's your current motherboard? If there's any kind of upgrade potential possible in that system, knowing what the motherboard can handle will help right off the bat.
In general, I would say you probably need at least:
-- more RAM. I suspect you have a 32-bit version of Windows, so the max you can install is 4GB. However, while DDR2 is slower than DDR3 (& therefore much slower than the "new" DDR4), being able to have it potentially...