it is interesting for us to watch tv还是it is interested for us to watch tv。

第一句是正确地，英语中像 interesting和 interested 这类形容词修饰名词的时候，-ing 形式通常修饰事，-ed 形式通常修饰人

这句话中很明显 It 是形式主语，不定式是真正主语， interesting 修饰 to watch tv 这件事，所以，前者正确

Somebody is interested in sth .

sth is interesting .

It is interesting to do sth .