I have installed ESET NOD32 v4.0 on a Windows XP SP2 and I would like to install SP3. Do I have to uninstall NOD32 before I upgrade to SP3?
No, but it would be a good idea to disable the real-time scanning before running the upgrade. You don't want the virus scanner interfering with the installation and causing problems with the upgrade.
While it shouldn't cause a problem, you'll be in a bad way if it does.