Ulrik,
Depending on your version of Oracle (sorry, I couldn't find that information in your posts), you can query the data dictionary for the query execution plan. For example, in Oracle 9i, you have the following views:
V$SQL_PLAN
V$SQL_PLAN_STATISTICS
V$SQL_PLAN_STATISTICS_ALL
You'll probably be able to find more details via Oracle's
OTN Web site.
Good Luck,
Avi.