Is it safe to download iTunes on my laptop?

When I say “safe”, I’m not referring to the actual security of my laptop. I’m referring to the security of the music already on my iPod.
Here is the scenario: There are two computers in my house. One main one, and my laptop. The main computer has iTunes downloaded; its been there for years. But the computer is always so slow and sometimes it doesn’t work. So I wanted to download it on my laptop since I can get a free download on the iTunes website. If I download it onto my laptop and connect my iPod to the computer, will it get rid of all the songs already on there?
And another question is, will iTunes slow down my laptop immensely?