Ok. Recibí tu mail.
No sólo estaba mal codificado el archivo sinó que tambien estaba en ruso

Acá tenes la traducción:
Installing Sibelius 5.25.
1. Run the file "SibeliusEnglishInstaller.msi" folder in "Sibelius 5.1",
in emerged pop-up window click "No" ( "No")
Serial number of the copy Keygen'a (file "BLESSiNG.exe" folder in the "Keygen"),
pressing the first button Generate.
2. Then in the registration program must select the "By fax or phone".
3. Copy Computer Number (C **** **** **** **** ****), insert in Keygen,
click the second button Generate, copy the Registration Number (R **** **** **** **** ****)
together with the letter "R". Paste in the login window to the specified string.
The rest is filled to your liking.
4. After a successful run to close the program,
update the file "Sibelius51to525UpdateEnglish.msp" folder "Sibelius 5.25"
Done! Congratulations!
If you need plug-ins and extensions to Sibelius'u - mount the image file "Sibelius 5 Hybrid DVD.nrg"
and install it with the necessary.