LimeWire has no password feature. LimeWire doesn't use a login system or membership of any kind. It's been developed with anonymous connection structure in mind. The only thing that others can find out about you is your IP address.

If you want to prevent others from using the program, you can install it in an off-limits folder in Linux. With Windows (except XP) this is not possiblre. I might point out that there is nothing you have to protect in LW, so passwords are not necessary. That is, unless, you don't like people seeing your library files through the LimeWire browser or you have small children that might get into mischief on it. If you really need to prevent someone from using LimeWire on the Windows platform, you could just uninstall it and reinstall it when you need to use it. You configuration data is recorded and left behind in C:\Program Files\LimeWire so that if you reinstall it, you shouldn't have to update your settings a second time.

Hope this helps! :-)