Yeah, I already know that the 851.7kb ZIP files are actually virus, and I never download them.

However, whenever I go to my library, why are there always a whole bunch of them already there, all named after different programs?

I delete them, but they come back soon enough.

How do I stop these from downloading themselves without selecting them?

you may already be infected, by an earlier download that you didn't realize. scan your machine for viruses right away. while you're at it, might as well do an adware, spyware scan [daware and spybot r tops]. also, for prevention, its good policy to scan every file you download off the net [thru limewire or not] for viruses BEFORE you open/run the file.
stay safe.