Using my iMac in a country with a different power supply standard
Building on @penguinrob's answer, the specs for the 2007 iMac can be found on the Apple Support KB:


  Electrical and environmental requirements
  
  Meets ENERGY STAR requirements 
  
  
  Line voltage: 100-240V 
  AC Frequency:
  50Hz to 60Hz, single phase 
  Maximum continuous power: 200W (20-inch
  models); 280W (24-inch model) 
  Operating temperature: 50° to 95° F (10°
  to 35° C) 
  Storage temperature: -40° to 185° F (-40° to 85° C) 
  Relative
  humidity: 5% to 95% noncondensing 
  Maximum altitude: 10,000 feet
  


It looks like you should be able to get by with the IEC cable/adapter; the transformer can handle 100-240V, so you likely do not need an additional transformer.