Assuming that you're talking about the 13" 2010 MBP, they're both essentially the same system inside. Same CPU, same GPU, same everything.
Differences? Well, one's a desktop and one's a laptop. The mini has double the USB ports (4) as well as an HDMI port. Other than the obvious things that come with a laptop vs. a desktop, they're pretty much the same. Like I said, computationally, they're identical.