What would happen if I used a dual end USB cord to connect computers?

Nothing, I think.

Are you talking about a USB data transfer cable? You would use it to transfer data between the two computers. A rather useful thing to have lying around.

USB A to A absolutely zip!

Physically connecting 2 computers with a USB cable will not achieve anything. However, running software applications that call for such connection will lead to the desired result.

The point is, why do you need to connect 2 PCs and do you have the right application to the job.

I don’t need to hook them up, I was jsut curious.

@IchtheosaurusRex links to the correct USB transfer (or bridge) cable for that job.

A plain USB cable can fry both computers.

Here’s are a couple of items from the USB faq, from the group which sets standards for USB. Note that when they say “illegal”, they mean ‘not compliant with USB standards’. They do not mean ‘police will knock on your door’.

Q5: How can I connect two PCs to each other with USB?
A5: You need a specialized USB peripheral known as a USB bridge (sometimes called a USB to USB adapter) to do this. Without a USB bridge, connecting a USB port of a PC directly to another PC’s USB port can damage the computers.

Q6: You mean I can’t make a direct cable connection like a null modem?
A6: Correct. In fact, if you try this with an illegal A to A USB cable, you’ll short the two PCs’ power supplies together, possibly destroying one or both machines or causing a fire hazard. Even there were no danger to the machines from the problem with two power supplies, there still wouldn’t be any way to get the two PCs talking to each other, since USB doesn’t support that particular kind of communication. A reasonably priced solution to handle this need is the USB bridge.

http://www.usb.org/about/faq/ans5/