I have this PC (what an awesome resource) with the standard 320Gb HDD and 4Gb RAM, running W7 Ultimate. I'm actually quite happy with it though it's a few years old.
I have thought on and off about moving to SSD - I use the PC for work 8+ hours a day - but have no idea what to look at as modern SSD are all SATA3 which I am sure I don't have.

For instance I saw the Intel 335 240GB SSD which seems a decent price for 256Gb, but should I be looking at new models in the first place?