i found the right one this time, but i'm not sure if it will work the way you want it too
http://www.wdc.com/en/products/products.asp?driveid=501&language=en
and it's bigger that a conventional external hard drive
but
quote:
Performance Specifications
Serial Transfer Rate
USB 2.0
Serial Bus Transfer Rate (USB 2.0) 480 Mbits/s (Max)
Transfer Rates
Ethernet 10/100/1000 Mb/s capable