I don't know if Big Papi used steroids. I'd like to think that he didn't, since he's arguably the most fabled player in Sox history (who else nearly single handedly turned a potential Yankees sweep into the first World Series in 86 years?). However, whether he used PED or not, I don't think his recent woes are due to steroids. It'd be one thing if we looked at Brady Anderson's freak season where he hit 50 homeruns and never came close to that again; however, it's quite another when he goes into this huge slump. While steroid withdrawal should hurt Papi's power numbers, it shouldn't be hurting his average like this.
I really think his current woes are psychological. I think he came in so eager to prove that last season's injury problems were behind him, that he tried too hard and kept digging himself into a deeper and deeper slump.
However, it looks like things might be turning around for him. I hope so. If he starts hitting like he used to, this very good line up becomes great. Pair that with a pitching staff getting even better with the return of Smoltz, and I'd say it's likely that come October, the Sox may once again be World Champions.