Brent,
If you go to http://yourserver.com/Services/ you will see all of the web services available. Click on svcUserAdmin and navigate to QueueMailBoxMigration. This provides the web service specification and definitions for each of the parameters. In your particular case, USESLL and DELETECURRENTMAILBOX (which clears the destination mailbox, if it contains anything prior to the migration), require True or False values with no quotes. The USERNAME and PASSWORD are for the source mailbox. The IMPORTTYPE would be exchange2007orlater (again with no quotes).
I hope this helps!