3.4.7 should be out now.

LimeWire has never autorun on startup (so an option to disable it was never around). The feature crept into the installer accidentally before the option was added. The 3.5.X series should contain the option during install, as well as from the options menu when the program is running.

You can remove the autorun by going to Start -> Programs -> Startup and deleting the LimeWire icon.