My old PC didn't have two slots to mount the drive, but it did have two connections so I just put the new drive on a piece of pasteboard and plugged it in (just don't put it upside down, they don't like to run that way)
If that won't work then you can do a peer-to-peer ethernet connection, using a crossover cable. It might be fairly slow however. You also have to configure some settings that might be a bit daunting if you haven't done it before.
I think the software is 'direct cable connection'. See the help for your system for the specifics of your installation.