Many users of Windows Vista have been plagued with errors whilst trying to update their phone's software. However, there are ways to overcome these errors and still be able to update your software without having to install a different OS or use a different machine.
First of all, when you're updating your software, you'll most likely get an error that says "Nokia Service Layer Host Process has stopped working".
When you do get the error, just press 'Close program'. Now open the task manager by hitting Ctrl+Alt+Del and then terminate the NSU process. Your phone now has a blank white screen and doesn't respond to any keypresses, don't worry or panic, it's OK.
Make sure you don't disconnect your phone from the computer or alter it in ANY way when it becomes blank!
Now all you have to do is open NSU and run the update again and everything should work just fine.
Enjoy your new firmware!