To enter a hex character in Windows,
  - For systems like laptops that have the numeric keypad layed over the
    keys, press shift-NumLk, so that the numeric keypad is active.
  - Press and hold the Alt key
  - Enter zero, then the decimal value of the ASCII character you wish.
    See my ascii file.  EG Alt-097 is "a".
  - Release the Alt key.  The character appears after the Alt key is let go.

The quick list is
 Keypad   Displayed     HTML Entity
Sequence  Character  (complete list here)
========  =========  ============================
  0149              • or • or •
  0151              — or — or —  Good for  lines.
  0162              ¢ or ¢
  0163              £ or £
  0165              ¥ or ¥
  0169              © or ©
  0172              ¬ or ¬
  0176              ° or °
  0177              ± or ±
  0178              ² or ²
  0183              · or ·
  0188              ¼ or ¼
  0189              ½ or ½
  0190              ¾ or ¾
  0241              ñ or ñ
  0247              ÷ or ÷

Be aware that the key sequence required for a specific character is a decimal number that starts with a zero. For example, a n-tilde is alt-0241, not alt-241. But having said that, there ARE some 3-character sequences that do NOT start with a zero. See here for a complete list of 3- and 4-character keyboard sequences, where you'll find the ñ character for example as both Alt-164 & Alt-0241.

The four digit combinations can also be found in
     Start->Programs->Accessories->System Tools->Character Map
Clicking on a letter shows the Alt keystrokes in the lower right of the Character Map window and its name in the lower left. There are many, many "fun" characters you can find there and cut-n-paste to use them, but these only work in certain applications. For example, Windows numeric keypad sequences 242 & 243 get you the greater than or equals sign and the less than or equals sign respectively (≤ and ≥) if you're in Word or a DOS window, but not if you're looking at them in a web page. Here are the two Windows keyboard sequences
     242 = (EditPad Lite, IE & notepad show both as an equal sign)
     243 = (Word & DOS Shows ≤ and ≥ but with a more horizontal lower bar)