On XP start up explorer.exe pops up

So, on every start up, the explorer.exe window pops up to the system32 subdirectory. From the MS site, this basically means that it can’t find some file that it thinks it wants to start up. OK, fine, how do I figure out what it’s looking for so that I can correct this without a lot of trial and error? This is driving me nuts. OK, more nuts. Thanks