Officially it's SP3 or higher, good luck trying it on an unpatched system because it may or may not work. The system, if it is indeed SP2, is inherently unsafe because it is no longer supported by Microsoft (since July 2010) for updates, not until you install SP3.
Read here about end of support for SP2: https://community.mcafee.com/docs/DOC-1315
Read here for hints on how to install SP3 semi-painlessly: https://community.mcafee.com/thread/2007
By the way installing SP3 isn't the end of it, there have been dozens and dozens of updates since then as SP3 is quite old now. So make sure you keep updating until it's finished offering new ones. I know it's a pain in the you-know-what to do it, but once done the system will work better plus you'll have the peace of mind from knowing it's fully patched and you've done your part.
Make sure you are using the Microsoft Update option in Windows Updates to update everything, also that IE8 is installed regardless of whether or not you use IE. Many applications do use it, including McAfee.