To setup a trace that only views the last hour but does not run out of space requires the following:

15:00

JOB1-Step 1- The trace script (set to stop after an hour) approx 300Mb, with trc file saved with DATETIME stamp, i.e. 6NOV 2006 1500PM.trc

16:01

JOB 2 Step 1- DROP current table where trc was imported

step 2- use trace_table to import trc file