For Part 91, if you aren't rated in an aircraft requiring a rating then you can't log it as PIC. You can log landings and IFR but only as SIC. If it's Part 135 you can't log PIC unless you are listed as PIC on the paperwork, even when it's your leg.
That's what I have been doing. But it does count towards my IFR currency when I am the one shooting the approaches right? I didn't really think about till the other day, I just want to make sure I can stay IFR legal.