Set up a calculation field that computes a value you can specify as the sort field for your portal.
Something like this calculation field with a Number result type specified:
Case ( Type = "Driving" ; 0 ;
Type = "Identity" ; 1 ;
DateCreated will be converted into a very large number value by this calculation. The number will equal the number of days from 12/31/0000 to the date created.
Seems to work great thanx