Start -> Programs -> Accessories -> System Tools -> Character Map
This will allow you to choose a symbol to insert into text. There are a great number of fonts and symbols available. However, getting them to work online is another story. If you're using Firefox, you can "Type in accented letters, international characters or symbols into Firefox or Thunderbird, either simply by using a context menu (there being support for many languages), or quickly by keyboard macro (you can even define your own)"
That extension is here
If the computer looking at your text does not have that font available, it will not show up.
In XP, you can switch to a foreign language, but if your keyboard does not reflect what you're typing, it could be disastrous.
Ñ is made by using the alt key and numpad on your keyboard (not the numbers above the letters) You can use the extended ASCII chart at the bottom of this page