such thing?

You cannot just make one of those cables: the USB end has some circuitry in it to present the device as the correct type to the OS and to turn the USB signals into Ethernet. This is non-trivial.

If you were to buy one of these cables it would not make your printer network accessible unless:

1) The printer has drivers for this USB device. This is very unlikely as both the printer and this cable are "client" devices relying on a Mac or PC for the "host" part of the USB protocol.

AND one of:

1) The cable contains enough circuitry and logic to act as a network print-server. This is highly unlikely.
2) The printer already has a print-server built in and is willing to use that network print server over USB. This is also highly unlikely as if the printer had a print-server it would have an ethernet port and we'd not be having this discussion.

So in short: no chance, you need a (more expensive) USB network print server. For example something like this. Note I have no idea if it's any good: it was the first Google result!

 

Apples Airport extreme can also link HD's and printers to a network, traditional or wireless.
http://www.apple.com/airportextreme/sharing.html

 

good call but the imac doesn't look like the current model either nor does the cinema display at the mac pro, so who knows if this is saying anything or not.

 

It is nothing special. That graphic has been around for almost a year, it was first introduced when the Airport Extreme 802.11n and the Apple TV were in announced at MWSF 07. I think there was a MacRumors article on it.

As far as the OP's question is concerned, I bought one of these. It did not work with my printer, so I had to take it back. But it was very easy to set-up and works with the different wireless routers I tried it on (not just Linksys). I don't know if you have a wireless router or not, but the benefit of this device is the ability to place it anywhere in your house. It works with both USB and Ethernet printers, and can be attached to a wireless or Ethernet network. (although if you attach through Ethernet you can only attach a USB printer).