Answers
Thanks for this information, I appreciate it! I think we all agree that the rules are sometimes written in such a way that it's very easy to misunderstand. Below I wrote down my understanding of the information provided.
1: If the PIC performs the landing, can I still log the landing?
ANSWER: When the PIC 'operates' the airplane during his leg/landing you can't log this landing as an SIC since you didn't 'operate' the airplane. However this does make sense to me, as far as I can tell there is not a written rule that states the above! (correct me if I am wrong)
2: If the flight time is 3 hours and 2 of those hours were IMC, can I log these hours (actual instrument) on a flight when I am operating the aircraft as an SIC? Or can only the PIC log those hours?
Answer: Not only the PIC can log those instrument hours, the SIC can log these hours also even if he wasn't the PF but since a minimum of 2 crew is necessary in this case (multi crew jet) that rule is no longer 'effective'.
3: Can I log instrument approaches when I am operating the aircraft as an SIC? What if the PIC flies the approach, and I assist him in that approach? (basically you do an instrument approach together, it's just that one pilot is actually flying and the other pilot (sic) is providing information/call outs on the approach)
Answer: No you can't, according to FAR 61.51G you must 'operate' the airplane to log those approaches.