A similar story here. I have Limewire on my desktop computer at home and when I bought a laptop recently and started up iTunes on it there was Limewire and a shared library from my desktop - without me having put Limewire on the laptop.
It is a strange one, it seems like if there's a wireless connection in the house Limewire will make itself at home on any computer. I haven't investigated yet but I'm hoping there's a setting that will disable this. It's annoying that the default setting makes it do this, but, well, it is Limewire.