If I'm assuming correctly, you want to be able to combine these two lower end machines to make one better machine. Connecting them with an Ethernet cable wont do the trick. In reality, you can't really combine them unless they're identical hardware-wise (in which case I think you can make them into a cluster, but I'm not sure if you can do that with Windows or if it has to be a special Linux distro).
However what you could do is use both of them but for different tasks. For example, you could use one do more processor/memory intensive tasks (like rendering a video) and continue using the other for web browsing without the other tasks affecting it.
The problem with this is that you need space on your desk for two monitors, two keyboards, and two mice unless you set it up with a KVM switch to switch between the two machines.