Whats the current processor in your system as I cant see it listed.
Upgrading the CPU will depend alot on what your board can support and in my experience with an older system then its better to go for a new mobo, CPU and RAM or stick with your current setup. Mainly because you may only be able to get a processor thats a few hundred mhz faster for your outlay so not really worth it. Also if you buy a new setup then your going to get support for the latest tech.
Adding a second hard drive is a really simple thing to do.