I would have to know the version of SQL to know how to answer this.

For 2008+, you have CDC.

For SQL prior to that, they probably wouldn't like my answer, but I would make the schema identical to the original table, adding a column(s) to the original schema if needed to support the logging.

This allows me to use all existing code and procs on the logging table, and/or to UNION ALL the two tables in such code/procs.