Enter your DW name and password
Go to File>Server Settings
Enter www.dreamwidth.org in the server field
Enter your name and passwords in the proper fields, Hit OK
The drop-down box on the login screen should have two choices now (If not, quit & restart Semagic) Check Auto Login on the Livejournal Account but NOT on the Dreamwidth account. I tried it the other way around and it didn't work for me.
Log in, type your post, but instead of hitting the big POST ENTRY button, go to Journal>Post To Multiple Journals
Select your journals and post