We have now seen this a few times so ...
If you have Etrust antivirus V7.0 installed on your machine you may experience a situation where the whole system runs extremely slow after the change to daylight svings time ( DST ). A bug exists in the Etrust software that allows Inotask.exe to run at 100% CPU utilization. The resolution is to apply an update from CA which can be found here.
Basically you download the file, unzip it ( using the CA unzip program ) then stop all the Etrust services. Next, replace the files on the affected machine. For a server there will normally be 2 files to replace an don workstations just one. Restart the Etrust services again. The CPU should now return to normal levels.
The strange thing that we have found is that only certain machines are affected. Sometimes servers ( SBS2003 included ) and sometime workstations. No rhym or reason. Go figure.