Okay well first in Windows Explorer go to Tools>Folder Options go to the View Tab and find the option that says "Hide Extensions of Known File Types" uncheck that I like it to show extensions so I also hit apply to all folders then Apply then OK. Then well you will notice that the host file doesn't even have an extension so just rename by Right clicking and then add .txt then when you are done editing your host file you just remove the .txt and place it back in that directory where it came from remove the original one. You may want to back it (the original one) up and place it somewhere else on your hard drive.

EDIT: okay well I guess you don't even need to do those first steps up there but yeah I just like windows to show file extensions its dumb that it doesn't by default. but yeah just rename it and add .txt