Hi
Something like this in your query :
Surname: Right([MyFieldName],Len([MyFieldName])-InStr([MyFieldName]," "))
will extract all of the data after the first space. You can then sort on that. Be aware that if an entry has a name such as "Mary Anne Smith" then it will pick up "Anne Smith" instead of Smith.
Remember to use your actual field name.
HTH, Andrew