About extracting and decrypting:

My computer knowledges are VERY limited. After some attemts I managed to extract the gmapsupp.img using innounp.exe:
c:\11\innounp.exe -x c:\11\MapUpdaterAll616_1790.exe

Now I am trying to decrypt it and following the instructions - Uncompress,run fxor,replace A with D - I tried:
c:\11\fxor.exe c:\11\gmapsupp.img
Computer is working for some minutes, then the dos-window closes and gmapsupp.img stays encrypted.

What am I doing wrong? I am asking for an instuction for a dummy!