downloading youtube videos

I attempted to download a video today and ran across a dilema. I got it from youtube, to keepvid and onto my desktop without a problem. Then I had to download a converter from the internet. I did that but when I tried to access it on my desktop it kept telling me I needed another update/download which I agreed to. It told me the download would take 55 minutes. That seems crazy. Anyway, my point here is that I am a little nervous about downloading all the this stuff onto my computer. My computer has noticably slowed down after downloading Second LIfe and I am afraid to download anything else. But...I need to pass the class :) Anyone else having this dilema? Suggestions?