A couple of times now I have logged into Lime wire and it is already downloading songs that I didn't search for or want downloaded. At first I thought maybe my sister was doing it by my computer is password protected and I changed my password once already. Any one else have this happen to them and should I be worried?

Sounds like someone's got physical access to your computer. Having a password is not necessary if you know what you are doing with windoze, (very quick to reset a password, make an account then delete it after use.)Dunno about Mac security though.