iOS devices can only print directly to AirPrint printers.
I cannot find anywhere in Apple's AirPrint compatible printer list, nor in Dell's documentation, any mention whatsoever that the Dell c1765nfw is AirPrint-compliant, so I will charitably consider "the Dell people" misinformed.
To print directly from an iPad / iPhone you will need an AirPrint compatible printer or another device to act as a print server. That can be a Mac computer running Printopia ($19.95 with free trial) or handyPrint (donation - supported). The Mac must be "on" but may be asleep for them to work. Equivalent PC options may exist but you're on your own finding them.
You can also buy this standalone print server:
http://www.lantronix.com/it-management/xprintserver/xprintserver.html
These options enable you to use any printer available to your network, even older ones that may predate AirPrint by decades.
Otherwise you will need to buy an AirPrint printer or multifunction device.
I recommend you avoid Dell.