How should I export from iMovie '09 to Youtube?

Go to export using quicktime for the best possible settings. You can even go 1080p this way.

 

"Share > YouTube" is not enough?

It publishes it straight into your account, and lets you choose a resolution (from 4 choices) to use.

Also, I checked the page you referenced, and I found all of the steps applicable to my copy of imovie 09.

 

Not one of those choices is 1920x1080.

My guides may be helpful to the OP.

I found the link he posted accurate enough, although I wonder about the frame rate. Setting it to 30 for 24fps source isn't recommended as I understand it.

 

I think you need to update your guide. The size limit is now 1024Mb not 100.

 

Done. And to note, the limit is now 2GB.

 

my personal limit is 4 hours / 20GB, however iMovie doesn't actually check, it just automatically assumes your limit is 15 min / 2GB - so it makes this feature useless to me a lot of times