I did a test between Microsoft Forefront Client Security VS Trend Micro OfficeScan 8.0
Install both client into the MS Windows 2003 Server with SQL 2005 and MS Rights Management Services Server running.
Shown below are the memory utilize by both AV
So here we can see that Trend Micro and MS forefront have a tie! Both use the same amount of memory. But please bear in mind that the Forefront fail the spycar.org test. Therefore Trend Micro OfficeScan 8.0 is still a better choice.