Get a faster CPU, faster and/or more RAM, and SSD drive or two. The faster the PC the faster it renders. Pretty simple. It'd swap to an Intel i7 processor, those are faster than the Phenom CPUs. If you want to increase speed without upgrading any hardware, can't do that.
You can turn off any antivirus as well when rendering, can unplug from the internet while you do. Any other fluff programs that may be running, audio managers, backup assistants, etc...