If you are giving your users an open ended method to type in text you're never going to get good data. So my first suggestion is that you create a method to have a table that supports each of your combo boxes or one table that supports them all (depending on what type of things you want in them and what they mean). That way, when they select something it's from a list that can not be altered unless they specifically add an item, and after that everyone will see the exact same description:
for instance let's say you're choosing a car type, instead of storing Toyota, Toyta, Toota, etc which are (I assume) allowed in your current situation your table would hold a value of 1 for a 'car type' table like this:
Code:
tblCarType
CarID CarName
1 Toyota
2 Chrysler
3 Foord
Then if someone misspells a world (foord) you can correct it on the table with the misspelling one time and it will be fixed on all your records.
The only real (relatively easy) way to do a spell check on a combo box would be to do something like copy the text value of the combo box to a text field then perform the spell check which is a bit convoluted. Combo boxes aren't meant to be free-form type-in response fields. They're really mean to be a limited, uniform, list of possible responses.