See:

• http://support.microsoft.com/kb/306560/en-us - How to use the United States-International keyboard layout in Windows 7, in Windows Vista, and in Windows XP
• http://support.microsoft.com/kb/306993 - HOW TO: Use the Language Bar in Windows XP

Method #1 This link may be helpful for typing accented characters in emails: http://tlt.its.psu.edu/suggestions/international/accents/codealt.html

The numbers must be entered by using the keypad and not the numbers at the top of the keyboard. Unfortunately, if using a laptop without a separate keypad, it is necessary to first to press "number lock" (usually fn+scroll) and then use the numbers in the centre of the keyboard (shared with letters j,k,l etc.).

Method #2 The above method can be tedious, especially when using a keyboard without a separate keypad. Therefore, I adopt the following method: Press "start"

        "All Programs"
        "Accessories"
        "System Tools"
        "Character Map"

From the character map, select all the letters of interest. Paste these into an email (possibly as its title) and then save the email as a draft.

  When next writing an email which needs an accented character, all that is necessary is to copy and paste from the above saved draft (title) into the email being typed.  A little time consuming to set-up but quick and easy to use thereafter.

Partial Method #3 Be aware that all vowels with an acute accent (á,é,í,ó,ú) are available on most European keyboards by holding down the "alt gr" key (to the right of the space bar) and, at the same time, tap the required vowel key.

All the above methods work on "Yahoo Mail", using a laptop running on "Vista".

One solution is to switch to Chrome. It has no problems accepting accented characters if you have your keyboard set to US-International. Firefox doesn't seem to recognise this keyboard, functions as if you are using a standard US keyboard