screen sharing with ichat?

[hank smith]

hello can some one welk me threw how to use screen sharing?
I tried to do this with another mac user and I couldn't take control of his 
machine
I heard his voice over but I couldn't work with anything in his machine.
he also tried with mine and all he got was a image button in my window.
when we tried to go to something as simple as the doc my doc came up not his
can I get some help on using this feature?
thanks
Hank