Not simply, no. The theory of sharing computing power to perform a task is a fairly complex setup. You can create parallel processing, which processes lots of smaller tasks over lots of processors, but this isn't designed for home PCs.
For instance, companies that create computer graphics for films have places called Render Farms, that contain server racks full of processors and RAM. however, this is laid out in a hardware configuration designed for the purpose of sharing tasks, whereas home computers are designed to perform single tasks themselves.
There's no simple way, if any, to link directly to a PCs processing power from another PC, just to slave it. You could, with some computing knowledge, build a program that could distribute tasks between machines, but you will be limited by your networking speed, and the speed at which the main PC can distribute tasks to other machines. It is not a simple setup, and will require patience and a lot of background knowledge of how your PCs hardware works, along with proficiency in a programming language powerful enough to support such a task, so be warned.
I hope this helps.