Using VMware fusion I generally create new virtual machines using File->New->Import an existing virtual machine. I then select the ovf I have that I want to import from. I wanted to automate this process using vmrun and I was wondering how to register a new machine using this ovf.
You can't do it using vmrun. However, VMware OVF Tool is a command-line utility that allows you to import and export OVF packages to and from a wide variety of VMware platform products. Once you've imported the OVF, you can use vmrun to register the resulting VMX file, and do all the usual stuff with it.
Note that not all OVF files are equal. Some of them define vApps, which consist of multiple guests, and IIRC the tool will reject the input in that case.