Windows 7: Preventing an Arp Man in the middle attack

How can we prevent an Arp Man in the middle attack

Use Https

quite simply be careful what networks you surf on

In simple terms a potential hacker would need either physical access to your network, or control of a machine on your local network as only local attackers can exploit ARP's insecurities

Very good point.
But there are still ways that people can tunnel into your network if you have exploited software and hijack you that way, but you have a greater risk of your DNS being hijacked than MitMA...

What if the attacker has legal right to be on the network ?

then if you where in control of the network you could use something like ArpON or you could use DHCP snooping which essentially validates from a whitelist, some switch vendors like Cisco have Dynamic ARP Inspection.

so if ARP spooofing is likely then network admins can impliment monitor and control by various methods

personally I never use networks for sensitive logons where I consider ARP spoofing as possible or likely

How do I set this up on a network connected in this way. It's a home network so i don't have any cisco switches.

router/modem------swtich----All pc's

Do you have any spare computers sitting around with two network cards available?

Well yes, I have got one such machine, but it's has got no HD.

Does it have a floppy drive?