filtering groups

From: novice (anonymous_at_discussions.microsoft.com)
Date: 08/11/04 

Date: Wed, 11 Aug 2004 09:19:55 -0700

I need to write a query that will return the most recent
incident within a related group, but I want a value
returned for each instance of that group even if there's
only one event recorded for them.

Ex: The last transaction made by each buyer regardless of
how many transactions they have made.

I know this should be simple, but I'm not getting it
right. Thanks.