First of all you can do a tracert, to determine which segment it is on your network. Then, if you look up the MAC address in something like http://www.coffer.com/mac_find/, you can determine the vendor of the offending network device. If it comes back with Dell then at least you've narrowed it down to a dell device. - (if it is a windows machine, you may be able to 'manage' it from computer management)
The conflict may also be because your DHCP server has allocated an address that should have been reserved. Check out your DHCP server and it may give you more details. If this is the case, make sure your printer is not included in your address pool or is reserved.
Use Find My iPhone to track your device: Find My iPhone is a free application for iPhone and iPad owners that can help you figure out where your device is at any given time. Just install this app on your other iOS devices to start tracking your lost gadget.