OK, I just whipped up two Ruby scripts to do this: one to download all the entries from Blogger (as Atom feeds), and the other one to take a files with Atom feeds and post them to LiveJournal as entries. It may take some competence to actually use them. (You will need to be able to install the livejournal and Hpricot gems for Ruby, and since I use Linux I may not be that much help if you use Windows.)

I can e-mail them to you or something if you want.