When you use a .mac account in ichat, you can see your friends that use iChat *OR* any AIM messenger in Oscar. TOC is an older protocol, for example all classic (OS) messengers use TOC, thus you can't see them. They don't appear on your list.
You can use an AIM handle in iChat. If you want to keep using your .mac there, use Proteus or Fire or JSuperChat with it, and log in with normal AIM handle, using Oscar (or toc). When you are as AIM, you should be able to see both Oscar and Toc users. Also the lastest version (beta) of Adium can work in Oscar. In practise, anyone using old Adium, any messenger in Classic etc, are invisible for you when you are using .mac.