Depending on the version of your IE browser you can use either 'ieSpell' or 'Speckie' add-ons, that will underline the text you type where spell check is required:
'ieSpell' - can be used with IE7 / IE8
'Speckie' - works with IE9
Here is an example of 'Speckie' configuration. Once add-on is installed, go to 'Tools -> Speckie Settings'.
Enable 'Speckie' add-on on the pop-up window in order be able to reach the configuration page:
Please note that you need to go through registration process on the 'Speckie' Website in order the installer to be available for download.
If you use Mozilla Firefox browser, then it has a built-in spell check that should be enabled in the browser options:
Google Chrome browser does a spell check by default.