If you want to add words to a custom dictionary you should set the CustomDictionary property of the UltimateSpell
child control to a value such as "CustomEnglish". Now it will create a file called "CustomEnglish.dic" under the
UltimateSpellInclude\CustomDictionary directory of your web application, and will append words into this file
when the user clicks the Add to Dictionary button on the spell check dialog box, or clicks the Add to Dictionary item
in the suggestion popup menu for spell check as you type.

Note that you need to give Full Permission to ASPNET (NT AUTHORITY\NETWORK SERVICE in Windows 2003) on your
UltimateSpellInclude\CustomDictionary directory in order to write into the custom dictionary file.