2005 6cd 2 din replacement

Hi I've just ordered a 2 DIN SAT NAV RADIO to replace the 6 CD 2 DIN factory unit, I'm assuming that the car has a standard ISO connection but I've heard stores that if I try to plug in an after market unit with out special adapters I could damage the new unit is this true, do I need any this special, and can I get an infill panel to go around the new unit to fill the gaps.(its a 7in screen unit size 175 x 98 mm)