Here is a step-by-step guide for you to download and convert youtube videos:

1.Download, install, and run Xilisoft Youtube Video Converter http://www.xilisoft.com/youtube-video-converter.html by clicking ‘New Task’ under the ‘file’ menu or directly clicking ‘New’ button in the main interface.
 
2. Drag video files
Drag a YouTube video to Xilisoft YouTube Video Converter or drag a YouTube video to the ‘Drop Zone’. You also can directly enter YouTube Video URL to “URL” box in the “New task” window.
 
3. Select the output type
select one of the available pre-configured output formats in “Save as” drop list below ‘URL’.
 
4.Select the output destination
Click “Browse” button on the right of the “Save to” box, select the destination where you would like to save your output(converted) video file in the “Browse for Folder” that appears, and then click “OK”.
 
5. Rename the output file
Uncheck the “Use default file name” option and enter a new name for the output file into “Rename” box.
 
Tips: The “Use default file name” option is checked as the default.
 
6. ‘Download and Convert’ video
Click “ok” button to close the ‘New Task’ window, and then a new ‘downloads and conversion task ‘window will pop up automatically. Then you can start to download and convert videos by clicking ‘Start’ button in the main interface or you can click ‘Start’ under the ‘Action’ menu.

Tips:
     You can manage the tasks that have been added in the task list, such as “start”, “stop”, or “delete” the selected task in the main interface.

 
   

oh, yeah, dedanlion.
I'm happy now, because I wanna tell you a good news for you. yeah, there's free youtube video downloader 

maybe www.xilisoft.com has prepared you for such worry 

Xilisoft Download YouTube Video is free to download youtube videos. 

Here's the link to the .exe file; you can also get it on their site.

how about the speed? that is really important for me. if the speed like a snail, that will drive me mad. i do care about this.

They released Xilisoft iPod Mate, a pretty value pack for iPod. convert videos and music for iPod, rip dvd to ipod, and also copy or transfer or back up your iPods to your computer , even back to your iTunes.