Do you mean a number?
VAL(string) or CLNG(string) depending on your version will convert a string to a number. If the version you use supports the Cxxx functions, use those as they will be forward compatable.
Well VAL(string) will conver it to a numeric for you.
(replace string with your string value)
You can use it in a query or whatever, say your column is Nvalue
NewNvalue: val([Nvalue]) will make it a numeric for you.