I'm also applying to ER for the 2008 match. I figure that i takes about 3-4 weeks to get the score after your Step 2 CK date. The programs can upload applicant's files starting on Sept 1st. From what I understand about ERAS and scores, you can have your file ready and finished (all except Step 2 CK and CS scores) on Sept 1st or later and then once your scores come back, they will be automatically released to ERAS and so the programs will get them because of the constant updates. I'm taking my CK in mid-august and CS in the end of august and so my scores should be in by mid-to-late september. Most ER programs don't start interviewing until nov-december and so I think my plan should be ok. I've heard that ER programs don't start sending out interview invites until the MSPE is sent out which is in october (i think), but don't take this as fact.
dmitri