Applications :: Won't Find Screen Sharing Info / Between Two Computers

I'm going to be using iChat for the first time and want to use the screen sharing feature between two computers running 10.6. iChat's documentation (http://docs.info.apple.com/article.h.../en/17157.html) says:

"While every screen sharing connection uses encryption, the highest level of security requires both participants to have MobileMe subscriptions with encryption enabled. If this is the case, you will see a lock icon in the screen sharing window."

I'm wondering:

1. What is the difference between the encryption that "every screen sharing connection uses" and the enhanced security allowed with MobileMe accounts? How does this compare with, say, doing VNC over an SSH connection?

2. I understand that one can get a free MobileMe account which only has iChat capabilities. Does this free MobileMe account enable iChat encryption, or do I have to pay $99/year to get that?