Tony,
Here's the list of agents that are supported by the DLP Agent (per the 11.1 System Requirements Guide):
Symantec DLP Agents can be installed on computers running any of the following Windows operating systems:
■ Microsoft Windows Server 2003 (32-bit) with Service Pack 2 or Windows Server 2003 R2 (32-bit)
■ Microsoft Windows XP Professional with Service Pack 2 or Service Pack 3 (32-bit)
■ Microsoft Windows Vista Enterprise or Business with Service Pack 1 or Service Pack 2 (32-bit)
■ Microsoft Windows 7 Enterprise, Professional, or Ultimate (32-bit or 64-bit)
■ Microsoft Windows 2008 Enterprise R2 (64-bit)
Those are the operating systems that our QA teams have tested and certified. If you choose to try installing the 64-bit agent on XP or the 32-bit agent on 64-bit it may work, but it isn't something that Support will be able to assist with if you have problems.
I hope that helps clarify for you!