There is a popular tool called youtube downloader, it hasn't worked for me for a while though. Can't really say why though, it might be my system.
Ever since then I have been using tooble, you have to pay for that though.
@tyler77 - do you actually have a download link to your software?
"youtube downloader" is pretty generic, and a search leads to a big pile of unimpressive links.
Then, I'm not sure why you would mention software that "hasn't worked for me for a while though"
And (more relevant) - mcleanmuir is looking for a youtube downloader that will still work with OS X 10.4.11
Most that I see require 10.5 or higher.
There is an application on MacUpdate.com listed as YouTube Downloader 2.0. However, it appears to be some sort of scam. Clicking on the developer link takes you to a site that where you supposedly can download Free Files Downloader +. It appears that Free Files Downloader + is supposed to be a Java app, but there is no indication that you actually download anything.
what vids are you trying to download?
if its youtube and associated sites you just go into window in safari, click activity and highlight the biggest file in the drop down screen and download it from there