Thanks for the info, I'm on my laptop so can't check the key I was writing to exactly, but basically I was storing the arduino IDE version as the key and the exectable path for arduino.exe for that version
"Registry Key"/Arduino/Version/1.0.1.0 ExePath "C:\ProgramFiles\Arduino1.0.1
My applications need to be able to scroll through all versions of installed arduino so a key is created for each install as above.