I started migration assistant using wifi - can i stop and switch to firewire

You don't erase, what you do is simply stop the process and NEVER use Wi-Fi to migrate, it could take a week or more and no I'm not kidding. You can migrate using a cable, if you have a new Mac it doesn't have Firewire so you will need a Thunderbolt to FW adpater or use a USB cable.

You can terminate the migration, but the partially migrated account is likely to be corrupt.

Erase it and start over using FireWire.

The source computer's contents will not be affected.

I have the same issue. How do I stop a and how do I "erase"

Um. Mac mini has a FireWire port, right? So I just stop the wifi migration and restart with he cable? I just stopped it. But the target says its still transferring! It's ALIVE!

If you have a Mac Mini then why in the world are you posting on the iMac forum? I'd recommend you start your own thread in the Mac Mini forums, I"m sure someone is willing to assist.