Where can I find documentation on these registers? More specifically, on the one labeled "PC" in Dolphin's debugger? I found a page on it before but now I can't find it....
PC is Program Counter, It contains the memory address of the instruction that is going to execute.
There too many SPRs for Broadway to list (Dolphin does not list them all btw), your best route to to read whatever section in the Broadway Manual that covers the SPRs