If you have a Windows OS then you can also use the Character Map.
Start > All Programs > Accessories > System Tools > Character Map.
Click on the character(s) of your choice > Select > Copy > Paste and voila: Ñ
If you use the Alt + method, you’ll probably have to also press the Num Lock key so that the corresponding LED lamp on your keyboard is turned on, and then use the numerical key pad on the right side of the keyboard.
If this is something you’re going to want to do on a frequent basis, use the International Keyboard layout.
Start->Control Panel->Change Keyboard or other input methods -> Change Keyboards -> Add
Choose the United States-International layout.
Now you can type ñ by either ~ followed by n, or by alt-n. Note that this will also now require you type a space after ”, ’, and ~ if you actually want one of those characters.