>Is there any way to do a query on the Memo field for a text string and have the found text string in each different record highlighted when the dbf is browsed? Any help would be appreciated.

You may run this query the usual way, e.g.:
Select * From MyTable Where "qwerty"$MyTable.MemoField
Note that this query is not optimizable, i.e. will be slow for big table.
Grid highlighting can be reached by using DynamicBackColor properties evaluated again by "qwerty"$MyTable.MemoField