I have been using an IE add-in program for a few days and it seems to be helping. While not 100% (by any means), you can add your own words and avoid redundant notices of misspellings.

http://www.iespell.com has an add-in for your browser that allows you to check the spelling in forms, such as what this post is being done in. I would believe this would also work on a Web based intranet where your employees may be completing forms online.

It can be activated with a pull down menu under Tools and has an icon in the toolbar.