If it is a video file then you can convert it into 3gp or other format. But I think you tube supports 3gp format only.

You can use windows movie maker help you. You can also use a professional tool help you, convert you PowerPoint presentation to a certain format that can be accept by YouTube.

It's quite easy since you have tons of choices to do so. My suggestion is simple but effective. You can dowload an add-in program called PPT2Flash which allows you to convert FLV to video within steps.
You can dowload if here

I'm a videographer and a web developer and from what I know about video, I would urge you NOT to do this. PP is a slide show and slide show videos are not as effective at getting your message across as is a dynamic video that properly incorporates motion and audio.

Instead, start over, using your PP as an outline for your video production. You could hire a local wedding videographer at a very reasonable rate and have the benefit of his professional equipment and know-how.

I checked Presentation to Video Converter and it's nice tool and really simple.

You can use this tool to convert your PowerPoint to a YouTube video like MP4, AVI, and MPEG: Wondershare PPT to Video

Hope it helps.

Try PPT2DVD... It perfectly turns PowerPoint presentations to video movies and burns PowerPoint to DVD.

you can use media-converter online site. It will help you to create video file.