Listing something on ebay and need a short link, simply take the full url (e.g. http://cgi.ebay.com.au/Complete-Touch-Screen-Point-Sale-System-BRAND-NEW-/320584868917?pt=AU_CashRegisters&hash=item4aa458e435) and remove the title and the part after the itemID.
So your new URL becomes: http://cgi.ebay.com.au/320584868917
So your new URL becomes: http://cgi.ebay.com.au/320584868917