OK, sounds like layingback has more knowledge than I on this matter. NOTE: lest this lengthy discussion confuse anyone, if you ARE running ANY version of Poser 5, then you've ALREADY successfully cleared the "Interlok" hurdle: As uli describes, installing SR4 wouldn't cause any additional Interlok activity, nor any further touching of your boot sector. Wombat's disastrous experience baffles me - I see no way in which SR4 could cause that.