I didn't quite follow what you said Dave. A listbox returns a single value but you can also get the values of the other columns as long as you know the index. A quick loop through the columns would enable you "pick" and save the values.
IN A BOUND FIELD/FORM
if you have a field in a table of type text say
then if you have a listbox bound to this field, it will show the single value stored in the field - not multiple values
IN AN UNBOUND FIELD
you can select multiple values - but if you want to save them, you will have to store them in some data structure (array?), and even then you will probably lose them when you close the app
MULTI-VALUE FIELDS
it then occurred to me that in A2007, there is now a multi-value field (although I am not familiar with the details - and it is clearly non-relational) - but it occurred to me that maybe this might allow you to save ALL the values of a multi-value list box in a single field.
hope that all makes sense