Dell XPS 720 - Help?

[ToR]

Hi there!

First off, Hello! Apologies if this is in the wrong area of the forum or anything, haven't quite got my head around the place yet!

I need some help with my Dell XPS 720. I'd like a new processor, but I'm unsure what exactly I can/should get that is compatible with the pc and will run faster. The Device Manager tells me I have:

Intel(R) Core(TM) 2 DUO CPU E6850 @ 3.00GHz
Intel(R) Core(TM) 2 DUO CPU E6850 @ 3.00GHz

I'm unsure which processor I can buy that will be faster, and be compatible with the pc.
Also, I'd like to put another internal hard drive in the pc, as I only have x1 300gb hard drive in which is almost full. Preferably I'd like something like a terrabyte hard drive, but again, I'm unsure as to what to look for in terms of compatability?

Any help would be much appreciated.

Good day guys!