If you’ve been having problems screensharing over ichat with a friend, here is Apple’s recommended solution. It seems that if you have one type of account (say.. gchat) and your friend has AIM there will be some sort of incompatibility and you won’t be able to connect. Screen share should work if both parties have: AIM.com accounts, mac.com accounts, me.com accounts.
According to Apple documentation, the highest level of screen share encryption comes with getting a .mac account. It’s free, so sign up for one. While signing up you can uncheck the boxes for spam email newsletters, etc.
Setting up your account on iChat
Enter in your .mac account username and password. You should show up as Available in iChat. It should be fine if you are invisible as well, but the other person will need to know they can message you.
Add friend to your buddylist
Add your friend’s screenname to your buddylist, but make sure you add it to the matching account you have.
If you are email@example.com and your friend is firstname.lastname@example.org, make sure you add email@example.com to firstname.lastname@example.org‘s buddy list… and not bunny1@aim / bunny1@me / @gmail..
The two screensharing options should become available